UPDATE: I reached out to PSVANE and asked them about the 6L6 max dissipation. The documented 23W is a conservative rating to ensure reliability and longevity under standard operating conditions. They have conducted additional tests at 30W dissipation and gathered feedback from other users. Based on this, they can confirm that the Horizon 6L6 tubes can perform normally at this level of operation without issues.
Okay, let me say, you guys are geeks. I’m blown away. I know this isn’t your first rodeo but this video was for me. You’re engineer enough to design the project with schematic, machinist enough to build the housing and assorted parts, technician enough to put it together nicely and correctly diagnose and improve from parts you just had ‘lying’ around. Did I miss mentioning anything else? For a retired carpenter I’m so impressed. I can relate to building the cabinet but the other facets of your build are foreign to me. Is that a hobby or business? Again, very impressive.
Thanks for commenting. I appreciate the kind words. I do have a full time job as electrical designer and my shop is basically for hobby purposes and I do make and sell a few things to cover the cost of my tools. I’d rather be in my shop making things than watching TV. I’m mostly self thought on my fabrication skills. Cheers.
Hi Mike, I enjoy watching your build videos, you have a habit of making things look so easy! You obviously have many construction skills, as all of your amps are very neat and pleasing to the eye, but the main point is you have the space to work and the correct tools for the job! I have constructed a couple of the Kegger KT88 amps, following Mark of Blue glow Electronics, and they sound very nice, to my Ears anyway. Amp building can become an addiction, but an enjoyable one!
Hi Mike, I used a 2x LM337's in constant current mode on the cathodes on the audio output tubes 6L6 push-pull on a 50 mhz xmitter. Nice about it is that it compensates for tube age and balance. Added some negative feedback to somewhat flatten the frequency response. I modified a Heathkit AA-22 stereo amplifier on all 4 output tubes the same way. Thermal camera imaging show that heat being dissipated on all output tubes are equal. (Ithink I set them at 22ma each at 275v plate voltage) 7w plate dissipation each, 6GW8.
Thanks for commenting. Great to hear about others doing similar things. I do like this amp and will “play” with it a bit. You have to start somewhere, test, measure and figure out what to do next. Cheers.
Thanks Paul. Yes, I have a milling attachment for my lathe. I know its limitations and does what I need it to do. Don’t have room for a proper milling machine! Lol. Hope you are doing well!? Cheers.
Thank you. What you see here is 20+ years of experience. I think if you start small, you could eventually get to something to this scale. My first projects were crude but you have to start and learn from somewhere! Cheers.
Thanks. Yes, you can pretty much swap those tubes in and it would work just fine. Of course the tube sockets and pin outs are different… but it will work! Cheers.
Yes. A 6SN7 is very close to a 12AU7. They both have a mu of 20. You could plug and play but double check the voltages and current before you run it. The concern with this circuit is you need 130-150v differential between the driver stage and the output stage. If you had 400v on the plate of the 6L6 you should have around 250-260v on the plate of the 6SN7. If you have a hot input source, the voltage swing will go high and do funky things to the 6L6. I hope that helps?
Nice video. It will be interesting to see how your tweaks go. Would you consider drilling so ventilation holes above the large resistors to allow cooling?
Thanks for commenting. The bottom will be a mesh screen and taller feet to allow for good ventilation. I did consider adding holes but it would take away from the look I was going for. The mesh will allow good airflow. Have a look on my community page. It will look the same as my EL84 amp. Cheers.
Hi Mike , to bypass the Philips copyright on their pentodes ..........the US developped the BEAM power tube .............these are not pentodes , so a tube labeld EL34 /6CA7 is an aberration , it's either a european pentode or a foreign ( US at that time ) beam power , the 6L6 family are beampower tubes . Thank you for the nice build and enjoyable video of your creations.
Thanks for commenting. I wasn’t aware of the complete history of how that played out. I’ve seen data sheets that refer to them as both so I’m not sure what this is about. Cheers.
@@MikeFreda It's a pleasure to share information.... Beam power tubes do not have a supressor grid ...instead these are terodes with extra beam focussing plates . The harmonic structure is different to that of pentodes........electrical they can be equivalent . These Horizon tubes look being well made ( for what are current production tubes ), people seem to be very happy with the results......
@@rickg8015 Could be. My homebrewed 6L6 SE amp runs at almost precisely 23 watts dissipation and so these tubes would be, according to their spec sheet, maxed out. I'm running Sylvania 6L6GC's right now, and they have about 1,000 hours on them so far with no problems.
Good question. Then again, rickg8015 may be onto something here! I do know that not all 6L6's are created equally. There are several variants and they do vary from each manufacture. The tube used is listed as 6L6WGC-AT. The W signifies to withstand greater vibration. I'm not sure if that also means less current output. Even the Datasheets have misleading information, like calling them a Pentode. They are actually a Beam Tetrode as someone stated in the comments below. I will do a deeper dive on this. cheers.
@@MikeFreda You're right about them being beam power tetrodes. And the W usually denotes a "military" tube, with stronger construction. As far as I know, all "GC" variants were rated for 30 watts. Earlier versions, like the metal 6L6, the 6L6G, 6L6GA, and 6L6GB all have 19 watt plates.
Awesome channel brother, love how you make it all from scratch! With the Psvane tubes, do you know what their claim is for this line? My understanding is they are made in China. Do they claim to last longer or be built better or something like that?
Thanks for commenting. At the end of the video I do a deeper dive on the tubes. Yes, they are made in China. This is considered a mid grade tube using some features from their premium line. From what I gleamed from their supplied literature these have a different base, new anode coating and improved internal structure for lower noise and microphonics. I hope that helps? Cheers.
Thanks for commenting. I haven’t heard that but I do intend to use this amp a lot so I will definitely follow up on how things go with these tubes and do follow up video on future mods of this amp. Cheers.
Thanks for commenting. For guitar amps, I typically do. For HiFi I typically don’t for a host of reasons. Cost. Different PT, I can use higher capacitor value for better filtration, Heat, noise, space and less voltage drop are a few. I don’t hate tube rectification, I just find solid state easier to work with. Don’t worry, I will use one in a hifi amp in the near future. Cheers.
Yes, I’m working on that. I accidentally fried my scope and working on getting a replacement and proper test equipment for these sort of measurements. Please stay tuned! Cheers.
Very impressive! I am considering going down the amp creator rabbit hole and this is perfect. Let me ask, what exactly is the difference between this amp and the boutique amps costing tens of thousands of dollars? This is a Class A amp I believe? New Sub here 👍
Thank you! The amp I build it true point-to-point where many mass produced or boutique amps use PCBs and proprietary PT's / OT's. Everything I was is easily sourced. They may also add some protection and better regulation to help with stability and possible warranty issues with people hooking things up wrong or the variance on the wall voltages. This is a Class A single ended amp. Cheers.
Hi Mike....I liked the video and of course the design for the amplifier...Would it be easy for you to send me the whole design / circuit..?? I'm just waiting for the lamps from the order and with a little patience I think I'll have it ready in a few days.....Thank you
Hello Mike, your video just showed up on my feed. Wow, excellent job on the chassis! I have several suggestions for the circuit design, and wondered if I could just E-mail you the info since it is a bit lengthy?
Thanks for commenting. Yes, please do and feedback would be appreciated. My email address is in the about section of my profile. You may have a hit the “more” button on my homepage to see. You may also have to subscribe to see it. Cheers.
@@MikeFreda Hi Mike, I finished the list I wanted to send you, however I tried every thing I can but, UA-cam won't display your E-mail. It makes me waste lots of time going through Captcha checking but, still won't display your address, it just keeps saying "try again". After 3 or so tries, it tells you the try limit has been exceeded.
Thanks for commenting. I’ve considered doing something like this but I’m not sure what to focus on. Do I start from the ground up from load charts or just focus on how to measure, calculate and adjust an output section? Would make for a lengthy (and dry) video. Cheers.
Hi, I noticed from the schematic that the second stage/second half of the 12AU7 is DC coupled to the first stage, but you use the volume pot as grid leak resistor. It seems risky to me not to give that stage a fixed grid leak res, as in case the wiper of the volume put loses contact through age/dirt, the grid is left 'in the air' and the cathode current of that stage goes out of bounds.
Thanks for commenting. Yes, that is a possibility especially if you have a budget pot. It doesn't hurt to have something like a 1m ohm resistor from wiper (pin 2) to ground. For safety sake, I'll add it to the linked schematic. Thanks again, cheers!
Yes, the sheath is heat resistant to a point. With a proper / quick soldering operation it will shrink slightly and stay in place. If you overheat it, it will eventually disfigure and melt a little. Cheers
Thanks for commenting. Yes, it is possible. It will work but I’m not sure if you will get full output. I have modelled it looked at load lines. You may need to raise the B+ on the plates of the EL34’s accordingly. Cheers.
@ thanks for the reply. I figured that the B+ on the EL34 would have to be somewhat higher to be optimal. I am rebuilding a Dynaco ST70 and will have an extra chassis and the original power transformer to start with. I am thinking that the stock power transformer would work well for a project like this. And due to the reduced demand on the transformer in both the heater demand and B+ current needs for an amp like this, that stock transformer would probably run reasonably cool. Unlike the hotter than Haitis mode in the ST70. I modded the amp back in 1990. I used it for several years before it got stashed away. It was working when I put it away, but like I said, it ran really hot. And when I got it out and looked it over, I found several components that were stressed from the heat and decided to use the Miller Audio kit and upgrade the power transformer to improve its performance and reduce the heat generated.
Thanks for commenting. Yes, you sure can do that. I'd probably go with a 12AT7 since the AX7 has a bit too much gain for this application. I did something similar in my EL84 amp. Bias the AT7 at 4-5ma, add some Plate to Plate Feed back and call it a day! The reason I went with 12AU7 is 1.) I wanted to try something different, 2.)12AU7 are a bit more linear (albeit have a lower Mu so I needed to cascade them), 3.) I had a pair and needed to figure out a way to utilize them. 4.) Its common for people to uses a 12AT7 to drive 6L6's and EL84 SE amps. Cheers!
Hi Mike I have a spare super reverb chassis with the transformers, tube sockets and filter caps. Would the power transformer 375-0-375 volts work with this design? I have 6L6GTs tubes as well believe not sure the difference.
Yes/No. To get the clean high output/headroom Fender uses high B+. It's common for these amps to have 455-465v on the plates of the 6L6's. If you wanted to use the parts you would need to tame the B+. A tube rectifier and some dropping resistors may get you there. Also, guitar amp OT's are different then HiFi OT's. They typically have a different frequency response and in a super reverb, it's a Push/Pull OT design not a Single Ended design as I have done. I would not re-use older filter caps. They also need to be a higher value... you will probably hear some hum emeniate. With some work, you could repurpose the PT, chassis and tube sockets but that's about it. Cheers
For info : The 6L6GC ( nos) has 30 watts plate..........7027A and 7581A have 35 watts plate ....So refering to the datasheet of the the Horizon tube...........do NOT use these in an amplifier using 6L6GC like a MC 240 and or other amplifiers designed for the 6L6GC or 7027A tubes ! A fabulous nice sounding tube is the nos 6V6G ( Marconi/GE )
Good point. Thanks for mentioning that. I’m not sure if their data sheet is a conservative rating or not but I would probably just stick to the tubes that the original manufacturer recommends. To be safe, I probably wouldn’t use these in a BF Twin or super reverb as well. They have very high B+ and bias.
@@MikeFreda Indeed to be safe ..........the original 6L6 WGB ( C is next evoltion is equivalent to the 5881 tube ( good sounding reinforced/reliable 6L6 tube but with lower votage ratings and reduced plate watts ° I would consider the WGC as a 5881/6L6WGB ) Have a nice day and always looking out for your videos.
Is there an ohms rating on that cat fire cable like 100 or 120? Is it sound good? you're going to put some global feedback what sort of speakers do you think you can drive impedance wise quite low?
Thanks for commenting. The Cat 5 i used is: #R7J604 Cat 5e 4PR 24AWG - type CM UL E126126-DG. I believe its 100ohms but I don't; think it matters since I'm only usine 12" of it. I haven't done any real testing of it. Its seems to work okay. I've been using Cat 5e cable for years. Yes, I plan to try negative feedback. I will employ/try Global and Plate-to-Plate. These are 8ohm output transformer but I suspect you are referring to speaker sensitivity. I don't listen to my music really loud so sensitivity numbers don't mean that much to me. It's more about the frequency response/curve and imaging. I've used 95dB full range, 92dB full range and 89dB Mission 761 2 way. They all sound great to me. Lower than 90dB you will notice the loudness. This is a lower wattage tube amp (~6 watts) so if you like really loud music, you may want to go with a Push/Pull design. cheers
hi mike ,i cant understand why r4 resistor 200 ohms instead a coupling cap resistors for voltage divider ,maybe im wrong but id like to understand this shematic,thanks
Thanks for commenting. The R4 200ohm resistors are Grid Stoppers. They help stabilize the grid and help block RF. The first two stages are direct coupled. One reason for this is to limit the amount of capacitors in the signal chain. Some people feel that too many capacitors inthe signal chain can "color" the sound. You can Google Direct Coupled amplifier stages for more info. You could add a capacitor here but you would need to change a few other things as well (i.e bias points and grid leak resistor) The 6.8k resistor and remaining electrolytic power supply capacitor is to decouple the driver section form the power section and provide a bit more voltage drop to lower the B++ on the plate of the 12AU7. I hope that makes sense? Cheers.
i wasnt to inform about driver direct coupled its new for me .i know how to calculate voltage drop and current in a circuit rc but im not sure to calculate well a voltage divider on your shematic.If i take rt=r1+r2 so 22k +6.8 k =28.8 k and 380v divide by 28.8k =13.1 ma travelling on the second half 12au7 so am right or wrong .So if 1icalculate the first half 12au7 this would be 328v divide 68k=4.8 ma ,i hope my calculations makes sense.thanks a lot
Sorry, I don't quite follow your calculations. The voltage drop across the 6.8k resistor is the combined current draw of each 12AU7 sections. V = I x R. V = (3.7mA + 3.8mA) x 6800. That is ~51 V. 380v-328v = ~52v . (The numbers are a bit off due to rounding off and multi-meter fluctuations upon time a measurement) I hope that helps? Cheers.
@@MikeFreda hi mike ok i understand how to calculate current for the first triode this is 328v -76 v=242v divide by 68k =3.7 ma but the second triode if i make the calculations 380v-328v =52v divide by 22 k =2.3 ma but you mention 3.8ma there is something that i missed probably.thanks
There needs to be more modern 6L6 and EL84 amps put out by manufacturers. It seems everything is 300B, 211 or kt88. Why not make tube amps that owners can source vintage tubes easily and cheaply? At least Elekit makes a nice 6L6 amp.
I agree, that's why people make their own. Lets face it, tubes amps are a niche market and 6L6 and EL84 are not considered audiophile grade tubes so people with go with 2A3, 300B KT88..etc since that's the industry standard and what everything is referenced off of. No profit margin for that sort of thing. Not to mention a lot of modern speaker are inefficient and to get high SPL number you need power... try to sell a 20-30 year old a 5 watt SET that sounds warm and glassy or a 200W Denon / NAD at a fraction of the cost that will rattle the dishes and have the neighbors call the cops. Cheers
I'm sure something like that happens. Those audiophile magazines don't pay for themselves! A good friend of mine was in the bike industry and the shenanigans favorable for reviews was prevalent. You buy and ad, you get a nice review one day. Cheers
UPDATE: I reached out to PSVANE and asked them about the 6L6 max dissipation. The documented 23W is a conservative rating to ensure reliability and longevity under standard operating conditions. They have conducted additional tests at 30W dissipation and gathered feedback from other users. Based on this, they can confirm that the Horizon 6L6 tubes can perform normally at this level of operation without issues.
Okay, let me say, you guys are geeks. I’m blown away. I know this isn’t your first rodeo but this video was for me. You’re engineer enough to design the project with schematic, machinist enough to build the housing and assorted parts, technician enough to put it together nicely and correctly diagnose and improve from parts you just had ‘lying’ around. Did I miss mentioning anything else? For a retired carpenter I’m so impressed. I can relate to building the cabinet but the other facets of your build are foreign to me. Is that a hobby or business? Again, very impressive.
Thanks for commenting. I appreciate the kind words. I do have a full time job as electrical designer and my shop is basically for hobby purposes and I do make and sell a few things to cover the cost of my tools. I’d rather be in my shop making things than watching TV. I’m mostly self thought on my fabrication skills. Cheers.
As always Mike, absolutely awe inspiring build. Thanks, for your effort.
Thank you, I’m glad you like it!
Excellent use of many disciplines, very impressed by your skill.
Thanks for commenting. I'm glad you liked it! Cheers
That's amazing, I've always liked valve amps they are really nice on the eye. Great job.
Thanks, tube amps do have something special to them!
Hi Mike, I enjoy watching your build videos, you have a habit of making things look so easy! You obviously have many construction skills, as all of your amps are very neat and pleasing to the eye, but the main point is you have the space to work and the correct tools for the job! I have constructed a couple of the Kegger KT88 amps, following Mark of Blue glow Electronics, and they sound very nice, to my Ears anyway. Amp building can become an addiction, but an enjoyable one!
Thanks 👍. Yes, Mark has some cool builds. He’s very informative. Building tube amps is addictive.. can’t stop at one! Cheers.
This channel is great, thank you for doing this. You are an inspiration.
Thanks, I really appreciate the support! Cheers.
Hi Mike, I used a 2x LM337's in constant current mode on the cathodes on the audio output tubes 6L6 push-pull on a 50 mhz xmitter. Nice about it is that it compensates for tube age and balance. Added some negative feedback to somewhat flatten the frequency response. I modified a Heathkit AA-22 stereo amplifier on all 4 output tubes the same way. Thermal camera imaging show that heat being dissipated on all output tubes are equal. (Ithink I set them at 22ma each at 275v plate voltage) 7w plate dissipation each, 6GW8.
Thanks for commenting. Great to hear about others doing similar things. I do like this amp and will “play” with it a bit. You have to start somewhere, test, measure and figure out what to do next. Cheers.
Excellent job and Video!!!
Thank you! Cheers!
Nice build!
Thank you. I’m glad you liked it. Cheers.
Mike, was that you using a lathe as a milling machine? Good video...
Thanks Paul. Yes, I have a milling attachment for my lathe. I know its limitations and does what I need it to do. Don’t have room for a proper milling machine! Lol. Hope you are doing well!? Cheers.
Wow you are so talented. I
wish i could do that
Thank you. What you see here is 20+ years of experience. I think if you start small, you could eventually get to something to this scale. My first projects were crude but you have to start and learn from somewhere! Cheers.
Nice work, Mike👍🏼.. I dig the chassis.. I hope you could design a 12/6SN7 front end version..
Thanks. Yes, you can pretty much swap those tubes in and it would work just fine. Of course the tube sockets and pin outs are different… but it will work! Cheers.
@@MikeFredaThanks Mike.. Would the input stage and driver stage plate currents be also around equal with the 6SN7?
Yes. A 6SN7 is very close to a 12AU7. They both have a mu of 20. You could plug and play but double check the voltages and current before you run it. The concern with this circuit is you need 130-150v differential between the driver stage and the output stage. If you had 400v on the plate of the 6L6 you should have around 250-260v on the plate of the 6SN7. If you have a hot input source, the voltage swing will go high and do funky things to the 6L6. I hope that helps?
Well done! Thanks for sharing🍻
Thanks for watching! Cheers.
Thanks Mike and PSVane.
You’re welcome! Cheers.
Awesome 👌
Nice video. It will be interesting to see how your tweaks go.
Would you consider drilling so ventilation holes above the large resistors to allow cooling?
Thanks for commenting. The bottom will be a mesh screen and taller feet to allow for good ventilation. I did consider adding holes but it would take away from the look I was going for. The mesh will allow good airflow. Have a look on my community page. It will look the same as my EL84 amp. Cheers.
Hi Mike , to bypass the Philips copyright on their pentodes ..........the US developped the BEAM power tube .............these are not pentodes , so a tube labeld EL34 /6CA7 is an aberration , it's either a european pentode or a foreign ( US at that time ) beam power , the 6L6 family are beampower tubes .
Thank you for the nice build and enjoyable video of your creations.
Thanks for commenting. I wasn’t aware of the complete history of how that played out. I’ve seen data sheets that refer to them as both so I’m not sure what this is about. Cheers.
@@MikeFreda It's a pleasure to share information....
Beam power tubes do not have a supressor grid ...instead these are terodes with extra beam focussing plates .
The harmonic structure is different to that of pentodes........electrical they can be equivalent .
These Horizon tubes look being well made ( for what are current production tubes ), people seem to be very happy with the results......
Well done 👍👍
I wonder why the plate dissipation is only rated 23 watts? RCA, Tung Sol, Sylvania, and even Svetlana 6L6GC's are rated at 30.
Might be lost in translation? Typical operation was labelled as max?
@@rickg8015 Could be. My homebrewed 6L6 SE amp runs at almost precisely 23 watts dissipation and so these tubes would be, according to their spec sheet, maxed out. I'm running Sylvania 6L6GC's right now, and they have about 1,000 hours on them so far with no problems.
Good question. Then again, rickg8015 may be onto something here! I do know that not all 6L6's are created equally. There are several variants and they do vary from each manufacture. The tube used is listed as 6L6WGC-AT. The W signifies to withstand greater vibration. I'm not sure if that also means less current output. Even the Datasheets have misleading information, like calling them a Pentode. They are actually a Beam Tetrode as someone stated in the comments below. I will do a deeper dive on this. cheers.
@@MikeFreda You're right about them being beam power tetrodes. And the W usually denotes a "military" tube, with stronger construction. As far as I know, all "GC" variants were rated for 30 watts. Earlier versions, like the metal 6L6, the 6L6G, 6L6GA, and 6L6GB all have 19 watt plates.
Awesome channel brother, love how you make it all from scratch!
With the Psvane tubes, do you know what their claim is for this line? My understanding is they are made in China. Do they claim to last longer or be built better or something like that?
Thanks for commenting. At the end of the video I do a deeper dive on the tubes. Yes, they are made in China. This is considered a mid grade tube using some features from their premium line. From what I gleamed from their supplied literature these have a different base, new anode coating and improved internal structure for lower noise and microphonics. I hope that helps? Cheers.
@@MikeFreda Sorry, didn't see the explanation at the end of the video, my bad. Thanks for the reply!
lots of premature failure in several of their tube types. sound great but terrible quality control.
Thanks for commenting. I haven’t heard that but I do intend to use this amp a lot so I will definitely follow up on how things go with these tubes and do follow up video on future mods of this amp. Cheers.
@@MikeFreda good luck
Hi Mike, nice build. You put a lot of quality into your work. Just curious why you never like to use a tube rectifier 5U4, 5AR4 etc. ?
Thanks for commenting. For guitar amps, I typically do. For HiFi I typically don’t for a host of reasons. Cost. Different PT, I can use higher capacitor value for better filtration, Heat, noise, space and less voltage drop are a few. I don’t hate tube rectification, I just find solid state easier to work with. Don’t worry, I will use one in a hifi amp in the near future. Cheers.
Where are the power, noise and distortion measurements?
Yes, I’m working on that. I accidentally fried my scope and working on getting a replacement and proper test equipment for these sort of measurements. Please stay tuned! Cheers.
Very impressive! I am considering going down the amp creator rabbit hole and this is perfect.
Let me ask, what exactly is the difference between this amp and the boutique amps costing tens of thousands of dollars? This is a Class A amp I believe?
New Sub here 👍
Thank you! The amp I build it true point-to-point where many mass produced or boutique amps use PCBs and proprietary PT's / OT's. Everything I was is easily sourced. They may also add some protection and better regulation to help with stability and possible warranty issues with people hooking things up wrong or the variance on the wall voltages. This is a Class A single ended amp. Cheers.
Hi Mike....I liked the video and of course the design for the amplifier...Would it be easy for you to send me the whole design / circuit..?? I'm just waiting for the lamps from the order and with a little patience I think I'll have it ready in a few days.....Thank you
Thanks for commenting. The links for the schematic and parts list are in the video description. I’m still working on the layout. Cheers.
Hello Mike, your video just showed up on my feed. Wow, excellent job on the chassis! I have several suggestions for the circuit design, and wondered if I could just E-mail you the info since it is a bit lengthy?
Thanks for commenting. Yes, please do and feedback would be appreciated. My email address is in the about section of my profile. You may have a hit the “more” button on my homepage to see. You may also have to subscribe to see it. Cheers.
@MikeFreda Thank you Mike, I will work on this tonight and try to send you something.
@@MikeFreda Hi Mike, I finished the list I wanted to send you, however I tried every thing I can but, UA-cam won't display your E-mail. It makes me waste lots of time going through Captcha checking but, still won't display your address, it just keeps saying "try again". After 3 or so tries, it tells you the try limit has been exceeded.
Nice build! instead of choke I propose to use gyrator. much better inductance, faaaar above choke!
Thanks. I've heard of gyrators in other electronic devices but never utilized in a tube amp PSU before. You use them?
Can you make a tutorial video on how to bias tubes?
Thanks for commenting. I’ve considered doing something like this but I’m not sure what to focus on. Do I start from the ground up from load charts or just focus on how to measure, calculate and adjust an output section? Would make for a lengthy (and dry) video. Cheers.
@@MikeFreda maybe on load lines and choosing a cathode resistor when you have a reactive load like an output transformer
Hi, I noticed from the schematic that the second stage/second half of the 12AU7 is DC coupled to the first stage, but you use the volume pot as grid leak resistor. It seems risky to me not to give that stage a fixed grid leak res, as in case the wiper of the volume put loses contact through age/dirt, the grid is left 'in the air' and the cathode current of that stage goes out of bounds.
Thanks for commenting. Yes, that is a possibility especially if you have a budget pot. It doesn't hurt to have something like a 1m ohm resistor from wiper (pin 2) to ground. For safety sake, I'll add it to the linked schematic. Thanks again, cheers!
hi the wire pvc ,is it sheath resist to solder iron without melt ,thanks
Yes, the sheath is heat resistant to a point. With a proper / quick soldering operation it will shrink slightly and stay in place. If you overheat it, it will eventually disfigure and melt a little. Cheers
Really enjoyed this project. Question though, would this front end provide enough swing to drive an EL34?
Thanks for commenting. Yes, it is possible. It will work but I’m not sure if you will get full output. I have modelled it looked at load lines. You may need to raise the B+ on the plates of the EL34’s accordingly. Cheers.
@ thanks for the reply. I figured that the B+ on the EL34 would have to be somewhat higher to be optimal. I am rebuilding a Dynaco ST70 and will have an extra chassis and the original power transformer to start with. I am thinking that the stock power transformer would work well for a project like this. And due to the reduced demand on the transformer in both the heater demand and B+ current needs for an amp like this, that stock transformer would probably run reasonably cool. Unlike the hotter than Haitis mode in the ST70. I modded the amp back in 1990. I used it for several years before it got stashed away. It was working when I put it away, but like I said, it ran really hot. And when I got it out and looked it over, I found several components that were stressed from the heat and decided to use the Miller Audio kit and upgrade the power transformer to improve its performance and reduce the heat generated.
Why not replace the input tube with a 12AT7 or 12AX7 with more gain, then introduce some NF from the output tx to the cathode of V1 ?
Thanks for commenting. Yes, you sure can do that. I'd probably go with a 12AT7 since the AX7 has a bit too much gain for this application. I did something similar in my EL84 amp. Bias the AT7 at 4-5ma, add some Plate to Plate Feed back and call it a day! The reason I went with 12AU7 is 1.) I wanted to try something different, 2.)12AU7 are a bit more linear (albeit have a lower Mu so I needed to cascade them), 3.) I had a pair and needed to figure out a way to utilize them. 4.) Its common for people to uses a 12AT7 to drive 6L6's and EL84 SE amps. Cheers!
Hi Mike I have a spare super reverb chassis with the transformers, tube sockets and filter caps. Would the power transformer 375-0-375 volts work with this design? I have 6L6GTs tubes as well believe not sure the difference.
Yes/No. To get the clean high output/headroom Fender uses high B+. It's common for these amps to have 455-465v on the plates of the 6L6's. If you wanted to use the parts you would need to tame the B+. A tube rectifier and some dropping resistors may get you there. Also, guitar amp OT's are different then HiFi OT's. They typically have a different frequency response and in a super reverb, it's a Push/Pull OT design not a Single Ended design as I have done. I would not re-use older filter caps. They also need to be a higher value... you will probably hear some hum emeniate. With some work, you could repurpose the PT, chassis and tube sockets but that's about it. Cheers
@@MikeFreda thank you for the tips, might as well sell these and get proper parts.
For info : The 6L6GC ( nos) has 30 watts plate..........7027A and 7581A have 35 watts plate ....So refering to the datasheet of the the Horizon tube...........do NOT use these in an amplifier using 6L6GC like a MC 240 and or other amplifiers designed for the 6L6GC or 7027A tubes !
A fabulous nice sounding tube is the nos 6V6G ( Marconi/GE )
Good point. Thanks for mentioning that. I’m not sure if their data sheet is a conservative rating or not but I would probably just stick to the tubes that the original manufacturer recommends. To be safe, I probably wouldn’t use these in a BF Twin or super reverb as well. They have very high B+ and bias.
@@MikeFreda Indeed to be safe ..........the original 6L6 WGB ( C is next evoltion is equivalent to the 5881 tube ( good sounding reinforced/reliable 6L6 tube but with lower votage ratings and reduced plate watts ° I would consider the WGC as a 5881/6L6WGB )
Have a nice day and always looking out for your videos.
Is there an ohms rating on that cat fire cable like 100 or 120? Is it sound good? you're going to put some global feedback
what sort of speakers do you think you can drive impedance wise quite low?
Thanks for commenting. The Cat 5 i used is: #R7J604 Cat 5e 4PR 24AWG - type CM UL E126126-DG. I believe its 100ohms but I don't; think it matters since I'm only usine 12" of it. I haven't done any real testing of it. Its seems to work okay. I've been using Cat 5e cable for years. Yes, I plan to try negative feedback. I will employ/try Global and Plate-to-Plate. These are 8ohm output transformer but I suspect you are referring to speaker sensitivity. I don't listen to my music really loud so sensitivity numbers don't mean that much to me. It's more about the frequency response/curve and imaging. I've used 95dB full range, 92dB full range and 89dB Mission 761 2 way. They all sound great to me. Lower than 90dB you will notice the loudness. This is a lower wattage tube amp (~6 watts) so if you like really loud music, you may want to go with a Push/Pull design. cheers
hi mike ,i cant understand why r4 resistor 200 ohms instead a coupling cap resistors for voltage divider ,maybe im wrong but id like to understand this shematic,thanks
Thanks for commenting. The R4 200ohm resistors are Grid Stoppers. They help stabilize the grid and help block RF. The first two stages are direct coupled. One reason for this is to limit the amount of capacitors in the signal chain. Some people feel that too many capacitors inthe signal chain can "color" the sound. You can Google Direct Coupled amplifier stages for more info. You could add a capacitor here but you would need to change a few other things as well (i.e bias points and grid leak resistor) The 6.8k resistor and remaining electrolytic power supply capacitor is to decouple the driver section form the power section and provide a bit more voltage drop to lower the B++ on the plate of the 12AU7. I hope that makes sense? Cheers.
i wasnt to inform about driver direct coupled its new for me .i know how to calculate voltage drop and current in a circuit rc but im not sure to calculate well a voltage divider on your shematic.If i take rt=r1+r2 so 22k +6.8 k =28.8 k and 380v divide by 28.8k =13.1 ma travelling on the second half 12au7 so am right or wrong .So if 1icalculate the first half 12au7 this would be 328v divide 68k=4.8 ma ,i hope my calculations makes sense.thanks a lot
Sorry, I don't quite follow your calculations. The voltage drop across the 6.8k resistor is the combined current draw of each 12AU7 sections. V = I x R. V = (3.7mA + 3.8mA) x 6800. That is ~51 V. 380v-328v = ~52v . (The numbers are a bit off due to rounding off and multi-meter fluctuations upon time a measurement) I hope that helps? Cheers.
@@MikeFreda hi mike ok i understand how to calculate current for the first triode this is 328v -76 v=242v divide by 68k =3.7 ma but the second triode if i make the calculations 380v-328v =52v divide by 22 k =2.3 ma but you mention 3.8ma there is something that i missed probably.thanks
ok mike i i understand its 328v-243v =85v divide by 22k =3.8ma now i learned something more on the calculations thanks a lot @@MikeFreda
There needs to be more modern 6L6 and EL84 amps put out by manufacturers. It seems everything is 300B, 211 or kt88. Why not make tube amps that owners can source vintage tubes easily and cheaply? At least Elekit makes a nice 6L6 amp.
I agree, that's why people make their own. Lets face it, tubes amps are a niche market and 6L6 and EL84 are not considered audiophile grade tubes so people with go with 2A3, 300B KT88..etc since that's the industry standard and what everything is referenced off of. No profit margin for that sort of thing. Not to mention a lot of modern speaker are inefficient and to get high SPL number you need power... try to sell a 20-30 year old a 5 watt SET that sounds warm and glassy or a 200W Denon / NAD at a fraction of the cost that will rattle the dishes and have the neighbors call the cops. Cheers
@@MikeFreda I think tube makers and amps makers talk behind the scenes to plan for the biggest profits by making only amps using high cost tubes.
I'm sure something like that happens. Those audiophile magazines don't pay for themselves! A good friend of mine was in the bike industry and the shenanigans favorable for reviews was prevalent. You buy and ad, you get a nice review one day. Cheers
@@MikeFredatalking about bike ads and reviews, that is true. Eff it all, I just want to listen to tubes.
That has to be 7 pounds per Watt! Pretty neat though.
Yes, it is a bit heavier than it needs to be. the side are pretty stout! lol Cheers.
Hey, dude, slow down! I can barely make out what you're saying!