Recent Posts

51

Tube Amp Building - Tweaks - Repairs / Re: A small friedman-inspired amp using an inexpensive power supply

« Last post by DummyLoad on April 19, 2026, 11:34:56 am »

Yeah, I saw that same pattern PS on Ebay as well, seems like several accounts to same vendor, USA stock BS, etc., bulk ordered and shipped from China; why they state the 4-7 days ship transit time. 


On the unit I have, adding the 6.3V load did not change things. Test results in link.  3x 10Ω 5W resistors in parallel, for 3.3Ω total load, or about 1.92A current load. Some of the resistors were cooking at ≈130°C. 


--Pete

52

Tube Amp Building - Tweaks - Repairs / Re: A small friedman-inspired amp using an inexpensive power supply

« Last post by AX84CH on April 19, 2026, 05:59:52 am »

The one I got appears a little different from the one in your picture

https://www.ebay.com/itm/157252283200

53

Tube Amp Building - Tweaks - Repairs / Re: A small friedman-inspired amp using an inexpensive power supply

« Last post by AX84CH on April 19, 2026, 05:55:13 am »

I have one on my bench as I type this doing a burn-in. Have only a resistive HT load on it, 4x 300Ω 25W resistors in series; the stack measures 1190Ω total. With that load the PS delivers 285V, so the calculated current draw is ≈240mA - Meh! typical Asian over-reach spec hype. I just viewed a video another buyer posted just a bit ago and they were seeing similar results. So, probably will return it and leave a 2-3 star review with my eval.

Link to lab results

--Pete

Hey Pete-

I notice you don't have a load on the filament supply.   I don't know if it is the case on the one you have but the B+ on the one I have seems to behave better with a load on the filament supply.

I will get around to testing both of these a little more.

Also on the one I have, as I increase the current demand by biasing the amp hotter, the plate voltage is creeping up a bit.  I think it was 285 with ~110mA versus 280 with ~70mA

54

Tube Amp Building - Tweaks - Repairs / Re: A small friedman-inspired amp using an inexpensive power supply

« Last post by DummyLoad on April 18, 2026, 06:23:47 pm »

This is the one I'd zero in on... 30bux. 300V @ 300mA; enough for 20-25W amp without working it too hard.

Still, I prefer linear PS for tube amps. JMO.

--Pete

I have ordered one of these to try and should have it shortly.   I'm not sure it will be radically different though an extra 20v is welcome. 

I would probably prefer a linear supply as well, all else being equal.   If these end up being workable for a segment of projects, they are considerably less expensive and lighter than a linear supply.  Of course, everything is a tradeoff.  I'm pretty happy with the amp I built so I would say it has been a general success.

I have one on my bench as I type this doing a burn-in. Have only a resistive HT load on it, 4x 300Ω 25W resistors in series; the stack measures 1190Ω total. With that load the PS delivers 285V, so the calculated current draw is ≈240mA - Meh! typical Asian over-reach spec hype. I just viewed a video another buyer posted just a bit ago and they were seeing similar results. So, probably will return it and leave a 2-3 star review with my eval.

Link to lab results

--Pete

55

Other Topics / Re: Meme of the day

« Last post by shooter on April 18, 2026, 02:40:35 pm »

 

56

Other Topics / Re: Meme of the day

« Last post by EL34 on April 18, 2026, 01:48:29 pm »

.

57

Other Topics / Re: Meme of the day

« Last post by shooter on April 18, 2026, 06:56:54 am »

...

58

Tube Amp Building - Tweaks - Repairs / Re: Revisiting Sears Silvertone 1484/85 Piezo Tanks.

« Last post by scstill on April 17, 2026, 04:34:41 pm »

I rebuilt the 1484 reverb tank a few years ago. It came out really good. I like it a lot.
Discussed at the link below, also some discussions on that subject in this forum.
https://stillampd.com/silvertone-1484-restoration

59

Tube Amp Building - Tweaks - Repairs / Re: Groove Tubes Soul-o 45 Rev B 1997 8 18 blowing main fuse

« Last post by shooter on April 17, 2026, 11:53:38 am »

ideas on what this is a symptom of, given what happened originally and what's been fixed?

 


did you save your notes??
start with the basics;


monitor the bias voltage at idle, NO signal, NO PA tubes, n evaluate

60

Tube Amp Building - Tweaks - Repairs / Re: Groove Tubes Soul-o 45 Rev B 1997 8 18 blowing main fuse

« Last post by wsscott on April 17, 2026, 11:33:42 am »

Well, I spoke too soon.  Bad news.

My buddy took the amp to a rehearsal last night to see how it would do, and he said it was fine until about 1/2 way through the rehearsal, I'm guessing maybe an hour, and then it started breaking up.  The guitar signal started cutting in and out, and it was making some weird hissing noises.

Any ideas on what this is a symptom of, given what happened originally and what's been fixed?

Thanks.