Recent Posts

11

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

« Last post by Sonny ReVerb on July 27, 2026, 01:40:10 pm »

Well, I dug into the amp today. I had already removed that fixed bias circuit for the PI, so that wasn't the problem. I retraced the circuit. I didn't find any wiring problems or incorrect components. I used a 100 ohm tail resistor and a 3300 ohm NFB resistor from the 4 ohm speaker tap for the NFB circuit. I tried disconnecting that. No significant change. I'm not sure there's a real problem, because everything works. It just doesn't seem as loud as it should be. I ordered some CTS "J taper" 1 meg pots. I'm going to replace the Alpha volume pots. Maybe that will make me happy...?

12

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

« Last post by sluckey on July 27, 2026, 09:59:49 am »

What tubes are those?

one tube. 7199

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

« Last post by Willabe on July 27, 2026, 08:59:03 am »

What tubes are those?

14

Other Topics / Re: Meme of the day

« Last post by shooter on July 27, 2026, 08:47:43 am »

...

15

Tube Amp Building - Tweaks - Repairs / Re: Princeton Reverb circuit refinements

« Last post by tristanc on July 27, 2026, 06:56:55 am »

I couldn't leave it alone....

• Reflowed basically all the joints. No difference.
• Tried playing with the bias again, on the assumption that perhaps there is cross-over distortion. Potential improvement. Instead of aiming for 70% I went to 80% That _seems_ to have made the issue less noticeable.
• Modified the reverb mixing components - the 3Meg and 10pF - based on a forum post of someone describing a similar distortion issue. Potential improvement. I clipped in a 68pF across the 3Meg (so 78pF) and to my ear, the extra treble made things sound better at 10/10 and provided just a bit more bite at lower volumes. The extra bite can be taken away with the treble control. It may be masking the harsh distortion, though.
• Clipping in a 1Meg in parallel just made things louder and the reverb not so good.

So I'm going to leave it biased hot for a few days and see how I get on. Next up, replacing the 10pF with a 68pF - may have to simulate that to see the implication...

16

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

« Last post by separateness on July 26, 2026, 08:18:44 pm »

Any of you fellas ever seen a cathode follower with a plate resistor?  See attached pic of an oil can unit schematic.  I have a similar unit with a different branding and basically electronically identical except for that resistor and cap on the plate of the cathode follower. I was just wondering why they'd gone and done that.

17

Buy - Sell - Trade / Re: Tube Tester TV-3 C/U

« Last post by triode on July 26, 2026, 08:02:03 pm »

PM Sent

18

Buy - Sell - Trade / Tube Tester TV-3 C/U

« Last post by jim on July 26, 2026, 02:17:27 pm »

This unit is manufactured by Jetronic Industries of Philadelphia in the mid 50's.   It works great and has served me well. It has a thumb wheel scroll that contains test perimeters as well as a VTVM which I never used.Plate cap, test leads for the VTVM, and power cord are stored in a compartment.  $150.00 and pick-up only (north of Baltimore)

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Other Topics / Re: Meme of the day

« Last post by shooter on July 26, 2026, 08:31:16 am »

....

20

Tube Amp Building - Tweaks - Repairs / Re: Vox AC15 based on Hoffman AC30 layout

« Last post by sluckey on July 26, 2026, 05:53:20 am »

No preference. I've always just used an 8K OT.