Recent Posts

1

Tube Amp Building - Tweaks - Repairs / Re: Cathode follower with a plate resistor

« Last post by Merlin on July 28, 2026, 04:06:43 am »

Any of you fellas ever seen a cathode follower with a plate resistor? 

Yep, useful when you want low output impedance but you also want to limit the output swing for safety reasons. Although I don't quite understand the rationale for it in the Duette

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Tube Amp Building - Tweaks - Repairs / Re: Cathode follower with a plate resistor

« Last post by separateness on July 27, 2026, 04:25:00 pm »

What tubes are those?

one tube. 7199

Correct, I should have said this to begin with.

Standard grounded cathode amp, not a follower per-se. Signal tapped for lo-Z, low level output from from cathode. Like follower, output phase follows input phase.

--Pete 

What exactly is the distinction there?  The presence of a plate resistor?
How does performance differ? Is the gain diminished witht the plate resistor?  I would assume so but what do I know. The echo recovery on my unit is identical aside from the plate resistor and cap.  Do you it would be an improvement to implement the resistor and cap there?

3

Tube Amp Building - Tweaks - Repairs / Re: Single tube Reverb headache

« Last post by shaun on July 27, 2026, 03:59:19 pm »

Finally! I found the noise issue and resolved it easily once discovered. I sometimes wonder why I put myself through all the frustration, but then.... Yes! Like Christmas in my head.

The V3b cathode resistor and bypass cap - this is the return side of the rev tank - in this case, a 1.5k and 22uF. I had these tied to the same turret on the turret board as for the V3a cathode res and the V4a cathode res. I figured "well, they all go to ground, so no worries..." But yes, big worries. This caused big noise. But it disappeared when I moved V3b cathode res ground connection to the same ground point as the reverb tank return, instead of grounding it on the board with other preamp cathodes.

I connected the cathode res of V3b to the RCA reverb return lug, instead of on the turret board, and voila! All I can figure is that the V3b rev return cathode must behave quite differently from a regular preamp cathode because whatever it's doing, it interfered with other circuitry. I experimented with a variety of grounding combinations, and it seems to only be the rev return cathode that needs special attention.

I don't understand it fully - can anyone shine a light? Thanks, as always.

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Solid State / Re: ISO tech on Fl east coast to fix Marshall 3315

« Last post by shooter on July 27, 2026, 03:33:27 pm »

https://el34world.com/charts/Schematics/files/Marshall/Marshall_150w_3315_5150.pdf 


or not   

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Tube Amp Building - Tweaks - Repairs / Re: Why is this Princeton style amp not loud?

« Last post by wsscott on July 27, 2026, 03:14:26 pm »

I know exactly what you mean!  Been there--Am there!  Good luck.

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Tube Amp Building - Tweaks - Repairs / Re: Cathode follower with a plate resistor

« Last post by DummyLoad on July 27, 2026, 02:25:59 pm »

Standard grounded cathode amp, not a follower per-se. Signal tapped for lo-Z, low level output from from cathode. Like follower, output phase follows input phase.

EDIT: is also summing point for dry signal path. 

--Pete 

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Tube Amp Building - Tweaks - Repairs / Re: Why is this Princeton style amp not loud?

« Last post by Sonny ReVerb on July 27, 2026, 01:53:07 pm »

More pics

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Tube Amp Building - Tweaks - Repairs / Re: Why is this Princeton style amp not loud?

« Last post by Sonny ReVerb on July 27, 2026, 01:51:39 pm »

More pics

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Tube Amp Building - Tweaks - Repairs / Re: Why is this Princeton style amp not loud?

« Last post by Sonny ReVerb on July 27, 2026, 01:50:28 pm »

Updated pics

10

Solid State / ISO tech on Fl east coast to fix Marshall 3315

« Last post by jukelemon on July 27, 2026, 01:47:07 pm »

Hi all


Helping out a friend who can’t ship me their 3315. Lives in the Clearwater/St Pete area. Amp is DOA. Could be as simple as a shorted cap.


Thanks!