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Ha, yeah not the easiest of procedures, but if it's to be done, this is one of the ways. Hopefully, you have one of the JVMs where Marshall has corrected this issue. If it were my own JVM and I ran into these issues, I would likely pull the board and convert to a JCM800 or another amp, as the transformers are great for that type of conversion.

@@jloewenheim - my JVM is only about 5 years old, so… I’ve been all over the JVM mod forum, some are real simple, others not so much. Isolating pin 5 is really far out and that glass drill you found is GENIUS. My skill level is bright circuits and FX loop improvements. I’ll definitely pull my chassi and give it a good look. Thanks again \m/

Thanks for the note. I believe it was a 4 or 5H choke that is stock for Marshall

@@jloewenheim thanks

Thanks for the note. I have all 3 and the blues jr. In my opinion Pro Jr. sounds amazing stock, the others have a very narrow range where they can be dialed in. That changes once you make the conversion.

There are several techniques that I use nowadays, which are a nice improvement to how I did things at the the time of the first 2 videos. One can learn a lot by looking at how Dan Reeves, John Suhr and Soldano build their amps...

Thanks for the compliments. Yes, look forward to discussing with you more.

thanks for the note. 7 pins on your EL34? is one broken off in the socket? All EL34 tubes should have 8 pins. Anyway, if you have questions, feel free to email me : username@gmail

@@jloewenheim This fix worked beautifully! I think my Bias was at around 40 MV, I bumped it up to 70 and absolutely love the tone! This video saved my amp, Thank you sir.

glad to be able to help you find a solution!@@dansittler4619

Hey now, appreciate any and all feedback. I'm not sure what you are referring to as sloppy (there is a lot that could be better), but I hope others get something out of it. Happy Holidays

Thanks!

Hopefully, you can get it solved.

All valid points. The video was to demonstrate what one can do once these problems occur and how it is a good candidate to convert/build a tweed bassman in the existing cabinet and chassis. As you may have concluded, I am capable of repairing the typical issues mentioned and others, including those that are related to the dual power rail and comparator channel switching circuits (for all issues, it is likely closer to the list price for a new HRD). Nonetheless, thanks for watching an the feedback.

I could be wrong, but I think to this day Bogen is in New Jersey. I think that type of circuit with a Bax TS and such were fairly common for many a PA and other clean amps of this era.

There is no boost pedal. that is the straight amp, the boost effect is simply switching on a bypass cap for the second pre amp stage

This seems pretty advanced - do you have any tips/recommendations for a beginner?

@@d.lauzon I have 2 recommendations that are a bit easier. First, you can leave the circuit fairly intact, simply replace the capacitors, and then revoice a few of the stages to be a bit more guitar-friendly. This only requires changing a few resistors and caps, while otherwise leaving things in stock form in terms of layout. The other idea is to build a more common version of the 5f6a or marshall in a different chassis, then use the tubes and transformers from the bogen chassis in a manner that you can easily reinstall them in the future if you like. Use these for the build Either way, please email and we can discuss further offline. username@gmail

We all have bought them because they do sound pretty good, in particular the clean channel. The question is when they need to be repaired, is it worth it. That being said, it's hard to argue that the sound of the 59 bassman or the plexi is anything short of amazing

I do have them, and no that is not how it works out. Voltages are quite close to a 5E3. Do you mind emailing me so that I can send you the schematic and voltages? username@gmail

Thanks for the note. Any chance you can email me? username@gmail.com

Great question. I generally have not been adding/retaining either the loop or reverb, but there is a way to do it, and I have a method that I can go over. On the horizon is a video showing how to set up the +/-16 v regulated voltages, so that the op-amps and relays can be utilized for these functions and channel switching. Feel free to email me (username at gmail) directly if you want a further explanation.

Thank you so much....I will here.

i got a bit delayed, will try to show the rest within the next few weeks

Thanks for the comment. Although, the ideal application-designed FR-4/G-10 should not conduct, unfortunately, this is not always the case, as there several factors (usually thermal) that can bring about this phenomenon. I work in the semiconductor processing and fabrication world, and this is quite a common challenge. There are several academic and online articles you can look up regarding the thermal properties of this material, and the potential for expansion/contraction, which can lead to traces that would otherwise be isolated from each other, losing the ability to be insulated from one another electrically. Dr. Tube has a practical write-up on this related to Marshall PCB's www.drtube.com/modification/jcm2000-stable-bias-mod/

I worked in electronics, including pcb design for over 20 years, and have never even heard of this. How do you make glass conduct by "thermal" means? How does expansion/contraction decrease insulation? I know all about arcing and clearances for high voltage PAT testing, but that's not the case here. The cynic in me says Dr. Tube want to sell their kits. They certainly don't have any creditable description or evidence for FR4 becoming leaky on their website.

@@ricobass0253 I'm certain you are very qualified, and always made sure to take all necessary precautions in your designs, and your point about the epoxy itself is correct. If you have a better method to solve these issues, there is a large community of Marshall owners that were love to learn about it. The issues, as I understand them have to do with the expansions of the dissimilar materials; those being the traces vs the epoxy. PCBs are not only made of epoxy, as there are several other steps that go into making sure they are able to contain electrical circuits. From my experience (on modern fabrication which does not involve tubes) we encounter several issues on the more modern boards, where cost savings are looking to be achieved. Examples tend to be related to humidity in the substrate, deflection during layer curing, and general instability of the related traces and pads prior to advanced packaging. These and other factors lead to shorts and other problems, ultimately leading to PCB failure (think about the number of flat-screen TV's that fail because they need a board replacement). Nonetheless, I had to work on this amp for many hours before resorting to the brute force of isolating the components and having success. There are several tests, component replacements, and other methods that I did not go into for time's sake in the video. As a final note, I easily lost money on the time spent working on this amp. I also spoke several times with Dr. Tube, and he had no issues discussing how one would go about this on their own. Based on my communications with him, it is hard for me (having no affiliation with him) to see how this is a ploy to sell kits.

Thanks for the note. The short answer is yes, you can measure the voltages with no tubes in, and it is the safest way to do it because you can insert your test probe in the socket where the tube pin would go instead of having your hands near all the other circuitry from behind. Also, with no power tubes in, you do not need to have a speaker load connected. All that being said it is still dangerous, so be careful. You are correct that voltages will go up since they are not loaded down (but not a significant amount). The most important thing is that you have stable negative DC voltage in pin5, it will be somewhere in the neighborhood of (-)40-55 volts DC. Please feel free to email me directly if you want to discuss this further: username@gmail

@@jloewenheim Thank you very much on clarifying it and for giving precautions! Yes, I am aware of a potential danger and do know how to handle high powered equimpent for sure.

thanks for the note, the HRD is a good starting point for many, but yes converting it either to tweed/plexi or BF is a good idea to really get the most out of it

dave do you mind emailing my gmail account (username at gmail) and then I can send you whatever you need?

The mojotone 5f6a small parts kit is $185 US. www.mojotone.com/Tweed-Bassman-Style-Small-Parts-Kit?gclid=Cj0KCQjwmdGYBhDRARIsABmSEePuDjWy7v4kvK6eWUQfUp9U5b0xZ3Ikuttgijnu22jEvfI4-_J4ersaAqy5EALw_wcB And then depending on what you have tool-wise, probably another $50-100 is you are starting with nothing. This is a great amp to do this on because there is no real resale value on these amps, and you already have the most expensive parts: transformers and tubes. Feel free to reach out directly to me username @gmail.com, I can provide a lot of resources

@@jloewenheim hey man mind if I email you soon? I’m gonna order the parts kit for a 4x10 deville. I just picked up a broken one for cheap. I did fix the usually problems but honestly it doesn’t sound very good. I built a tweed champ and a single ended plexi from kits last year so I think I’m up for it ..

@@petheato3291 Anytime, glad to help. I am actually converting one as we speak, was eventually going to post about the variations and some new upgrades that I like to add to the conversion.

There are a lot of directions that you could go. Do you mind emailing me so that we could discuss what you are really looking to do? username @ gmail.com

Yes, thanks for the note. You will need to "Upgrade" to a bridge rectifier since there is no CT, nor 5v secondary to power a typical rectifier tube. Please email me and I will send you lots of useful stuff that I have been supplying others with who have also followed my lead on this. my username@gmail.

Good luck, feel free to reach out if you need any advice (username @gmail.com). Remember that there is a lot of juice in that power transformer (on today's mains), so you may need to play around with the cathode bias resistor value if you go that route.

@@jloewenheim I don’t think I’m sticking with the two 5y3’s. I think we’ve moved past that as a society;-). Solid state diodes and a resister for a bit of sag makes more sense I think. I’m tempted to keep the PI paraphase just because the bassman did alright with one for a while. The Bogen should be a nice change of pace from Hammond and Roberts reel to reel amps I’ve done for the past few months!

@@williambock1821 OK, so since this build, I have done a few more conversions, and my honest advice is as follows (conversions can be a pain and frustrating): Unless you are really determined to figure out how to keep the Bogen chassis and look, you pull the transformers and tubes, then use a more Fender/Marshall approach on the chassis and board. This gives you two advantages: first, you can now always drop the transformers back into the original if you want to sell it as such. Second, and more importantly, the fender style eyelet board (turrets too) will allow you to be very organized and methodical about your build, as well as, give you the room necessary for controls and other circuit options that go beyond what Bogen did. As for your rectifier (despite what Mesa advertises), the dual 5y3s make it run very hot, so there are advantages to going SS. At some point, I will put on some videos where I have started to use a VVR circuit. This allows those old PT's, which on modern voltages, often have secondaries around 400v, be used closer to the voltages we know. Additionally, it allows you to go SS rectifier without needing to rely on sag.

@@jloewenheim Thanx for the input! I’ve done four or five conversions with VVR’s and when they work well they work VERY well. Some circuits(I’m just talking about cathode biased amps) just get too fizzy to really get much use from them. I’m sure they could be made to sound better if I had more experience. So far , I can’t narrow the variables down to what makes a VVR sound too fizzy. Some sound great at low voltage levels and some sound like a wet fart,lol! The Roberts reel to reels sound great with them if you do a one 12ax7 going into the El84 like a 5 watt version of a Marshall 18watt circuit. The actual 18 watt lite 2b circuit in a Hammond Ao35 sounds good too. Not much luck with Hammond Ao44’s though regardless of the conversion (tried 5 different ones) done. I’m tempted to try one on the challenger. I have all the components on hand for exactly ONE more VVR!

@@jloewenheim I wound up turning it into a 5e3 with VVR and bias selector switch for 6v6/6L6GB’s. Replaced the burnt out OTX with a brand new 25 watt Hammond 1650F. Wiring the impedance selector was…interesting! Used F&T for B+filter caps and Jupiter everywhere else. Well,a Sozo silver mica was used for the bright cap. Wired it all point to point with creative use of a few tag strips. It’s the best sounding amp I’ve built out of around 25 so far! I wish I could keep it but it’s already paid for. I’m looking for another Cha 33 for myself! Just as an FYI, the cathode resistor needed to be upped to about 700 ohms for 10-11 watts (about 80% ) of plate dissipation for 6v6’s. The 6L6 GB’s needed 330 ohms for the same percentage of dissipation. Again, this is a 5e3 build.

I do. any chance you might email me at my (username@) gmail

Despite the guitar still hanging on my wall, unfortu lately there is no label and I do not know the model number. My understanding is that most of these are built similarly will ladder bracing and dovetail joints.

Hi Gary, I'm not sure that I understand your questions, as there is no pedal being used in this video. The possibility of a pedal is for the a/b/y which allows you to change from one channel to the other. It has no effect on tone quality.

Hi Mike, thanks for the comment. Although it likely looks like the 180 you are mentioning, they are using what is the 3 Digit resistor code, typically used for labeling SMD resistors. The code is "1R0", this link will explain how that works: www.hobby-hour.com/electronics/smdcalc.php Now to explain why they are 1ohm. the reason for that value is so that the voltage measured on the test points will be equal to the bias current (using the formula V=IR, if R=1, then V= I). Hopefully, that clarifies.

@@jloewenheim you've probably noticed that I figured that out by my comment edit. Thank you. What did you replace yours with? I figure I need something that can take the voltage and current, the schematic says 1 watt, and should probably be something that can take a lot heat. There are a million different 1 ohm resistors on digikey and mouser. Any suggestions?

@@rustyzipperband Hi Mike, glad you were able to figure it out. I actually prefer to use 2 or 3-watt 1% resistors metal (3w are what I have at the moment), in particular when it comes to EL34 loaded amps. As you mentioned, you can use the general supply companies like Digikey and Mouser, you can also go to the amp supply companies like Mojotone.

@@jloewenheim awesome! Thanks for that info. There is nothing more frustrating to me than shopping for parts on digikey and mouser. If you have any other alternatives please do share. I've been a hobbyist for over 10 years building effects. I also built the guitar in my profile pic along with many others. I used to go though Tayda, and ebay. I've avoided digikey and mouser till about a week ago.

@@rustyzipperband any chance you can send me an email? my username at gmail.

Thanks for the note. Please feel free to directly email me if you need any assistance. my username @gmail.com

Agree, that was why I decided to do the conversion. if in new condition, I likely would have left it alone until problems occurred.

that is definitely a symptom. That being said, one of your tubes could simply be bad, to eliminate that, switch tubes into the other socket. If this continues on the same socket its not the tube. I suggest you measure the bias voltage (will be negative DC) on pin 5 for each socket both with and without tubes in. If that voltage is not holding stable or is showing positive voltage, you likely are having the leak issue described. it is probably more likely to occur with the tubes in. Sounds like it is only on one socket, but if you plan to do the repair, you might as well do both. Also, feel free to email me if you like. username @gmail.com

Hi John, feel free to email me at my username at gmail.com. in short, I used 1N4007 diodes to rectify and left the reverb out. I have helped several folks doing these conversions and will gladly help in any way that I can.

@@jloewenheim excellent! am doing the conversion i will email you.. The iron in this has limited options (lack of center tap). Really wanna keep the reverb somehow. Thanks again!

@@johnmiller9219 Reverb can be kept, we can discuss when you are ready to build.

do you want to connect via email? my username at gmail.com

@@jloewenheim sorry for the late reply Yes will email Thanks

there are a lot of places, but what you want is 1ohm, 3 watt, 1% tolerance. Try tubes and more, tube depot, antique electronics, Digikey, Mouser, or arrow.

@@jloewenheim Thank You sooooo much, really appreciated! .... I almost used a 1 watt 1ohm 1%

@@mikeliotta7530 1Watt will likely work as well, but I like the 3 watt in particular if you are using an EL34

Hey thanx again man! Ordered afew 3watt.... Goin in my jvm410. Have a great & safe 4th of July, Bud!

You are correct, thanks for catching that. I also am not a fan of the 1w screen resistors. Nonetheless, out of the box, the HRD series is a pretty good bang for the buck amp. As I'm sure you know, they will eventually have problems, and then I think it is a good time to think about converting into something else....

@@jloewenheim I agree. Once you properly "set up" a HRD, they sound bloody awesome. I don't care for their sound out of the box.

You are right mate, this R470 use to work with zener diode to clamped 48V down to 16V that a lo of voltage drop over this resistors , the correct way is lowering voltage drop to reduce heat dissipation (Current=(48-16)/470, then calculate to power=2.178watts , so if reduce 48V down we gonna get lower heating, the easiest way is change C100uF to 15uF this help lowering dc voltage on rectifier to supply to these R, no more cooking. Hope this help.

Hopefully, you got my reply. I look forward to helping you make the conversion!