Great video Doc! Thanks for helping me understand tube amps. Sold my Maco 300 with new 8950’s . Rebuilding the the 300a Palomar it has the old style short 6 KD6’s got some new 6KD6’s and they are taller will need to extend the cover! My Elmer sold me a 2008 Amartron 811 three tuner for 400 bucks I’ll use that on 20 meter’s chow JohnBoyUtah KJ7TBR 🇺🇸😎🎙
Thanks for explaining the sizing of the plate and tune capacitors. Great idea , having a amplifier set up to test output tubes. As always said, “the best way to test a tube , is to test it in the circuit it’s used! Question: working on a Kenwood TS-830, in the final output circuit: they have a small 6.8 uhy choke in series from the power supply, connected to the cold end of the large RFC choke. The hot end of the larger choke is connected thru a blocking capacitor and then on forward to the parasitic suppressors to the plates. What is the purpose of the 6.8 uhy choke. Is it just to capture any residual RF that sneaks by the main RFC? It’s so small; the size of a 1/4 w resistor. Is it being used as a fuse to protect the larger main pi wound RFC? Why is it so much smaller in physical size compared to the main RFC? Keep they great videos coming, I certainly appreciate your lessons.
Yes thats exactly what that is for, to catch the stray rf that might sneak by, and also to make sure that there are no resonant frequencies from the choke's'.
Amps that are monoband don't have one, and many amps built for CB are just that monoband. Most Ham amps are multiband and have a rotary switch on the front that says something like l0 meters, 20 meters, 40 meters and 80 meters. Behind that rotary switch would be the Band switch. If you look at the very beginning of this vid and at the amp on the left, the band switch is still there but disconnected and is right behind the Tank coil. As these amps are monobanded, they don't need a band switch.
Never seen a cap on he tune Sue for more capacitance I’ve seen it to pad the load side but when you do that starts your pf higher as well. I’ve done it before messing around with air variables but wouldn’t keep it that way, one needs the correct of. Good video my brotha 👍🏻
Ita unusual to have one on the tune side as normally the PF's needed is so low, it doesn't need to be padded. However, if I had say a 5-35pf variable and I needed 50pf's in the circuit, I don't see anything wrong with adding something like a fixed 20pf. I also had an amp that was a Dentron 2000L with an 8877 with a HD Dahl transformer. The transformer upped the HV a lot and the factory tune cap was arcing. Since this amp was monobanded, the tune cap had a lot of unneeded extra pf's but not enough voltage rating. This amp had like a 100pf padder on the tune in Series. It worked, but tuning was a little twitchy. I replaced that scheme with a proper rated higher voltage tune cap and it worked a lot smoother.
What would you use to clean the variable air capacitors?
Excellent video
Blessings TramDr.i have a 300a and the load knob is suspect,it that part hard to replace?Help🙏🏿🙏🏿
Load Caps can be found.
There will be a quick test after this head spinning tutorial.
Great video Doc! Thanks for helping me understand tube amps. Sold my Maco 300 with new 8950’s . Rebuilding the the 300a Palomar it has the old style short 6 KD6’s got some new 6KD6’s and they are taller will need to extend the cover! My Elmer sold me a 2008 Amartron 811 three tuner for 400 bucks I’ll use that on 20 meter’s chow JohnBoyUtah KJ7TBR 🇺🇸😎🎙
Good stuff.
Cool ! Glad to see someone talking about Tube amps !
More to come!
Thanks for explaining the sizing of the plate and tune capacitors. Great idea , having a amplifier set up to test output tubes. As always said, “the best way to test a tube , is to test it in the circuit it’s used!
Question: working on a Kenwood TS-830, in the final output circuit: they have a small 6.8 uhy choke in series from the power supply, connected to the cold end of the large RFC choke. The hot end of the larger choke is connected thru a blocking capacitor and then on forward to the parasitic suppressors to the plates.
What is the purpose of the 6.8 uhy choke. Is it just to capture any residual RF that sneaks by the main RFC? It’s so small; the size of a 1/4 w resistor. Is it being used as a fuse to protect the larger main pi wound RFC? Why is it so much smaller in physical size compared to the main RFC?
Keep they great videos coming, I certainly appreciate your lessons.
Yes thats exactly what that is for, to catch the stray rf that might sneak by, and also to make sure that there are no resonant frequencies from the choke's'.
ALWAYS SHOW THE CIRCUIT DIAGRAM OF YOUR PROJECT PLEASE.
I'll try when I can.
@@tramdr yes tramdr schematic of whole amp please 🫵🏻
🤦♂️
Thanks for sharing the knowledge. Always a pleasure when you school a mud runner or two 🎙️🎙️🎙️
I'm a mud runner myself.
Where is the band switch?
Amps that are monoband don't have one, and many amps built for CB are just that monoband. Most Ham amps are multiband and have a rotary switch on the front that says something like l0 meters, 20 meters, 40 meters and 80 meters. Behind that rotary switch would be the Band switch. If you look at the very beginning of this vid and at the amp on the left, the band switch is still there but disconnected and is right behind the Tank coil. As these amps are monobanded, they don't need a band switch.
Cool. The knowledge will be passed to the next generation.
I'd be happy if a few more with this generation got it.
Never seen a cap on he tune Sue for more capacitance I’ve seen it to pad the load side but when you do that starts your pf higher as well. I’ve done it before messing around with air variables but wouldn’t keep it that way, one needs the correct of. Good video my brotha 👍🏻
Ita unusual to have one on the tune side as normally the PF's needed is so low, it doesn't need to be padded. However, if I had say a 5-35pf variable and I needed 50pf's in the circuit, I don't see anything wrong with adding something like a fixed 20pf. I also had an amp that was a Dentron 2000L with an 8877 with a HD Dahl transformer. The transformer upped the HV a lot and the factory tune cap was arcing. Since this amp was monobanded, the tune cap had a lot of unneeded extra pf's but not enough voltage rating. This amp had like a 100pf padder on the tune in Series. It worked, but tuning was a little twitchy. I replaced that scheme with a proper rated higher voltage tune cap and it worked a lot smoother.
Nailed it Doc.
Thanks.
Hey Tramdr, Another great informational video for the archives. Thank you.
You're welcome.
Great information! Your a good teacher. Thanks for taking the time to make the video. Nice tube tester too!
Thanks.