Tube Amp Archive

Nothing wrong with being curious as to the bias power supply wave form (ripple), but you do not need a scope to measure power supply ripple voltage which will change as you adjust the RC filters. Just set your meter to AC and keep in mind you are looking at ACRMS (Peak voltage *0.707).

Then I replaced the two section cap can that contained nodes 1 and 2 and replaced it with another I had in the parts bin. Unfortunately, same results. Still have 4.7 vac at the first node followed by very low millivolt readings at the remaining three nodes. You can calculate the expected ripple vol...

Couple of questions to clarify:

Jaydawg, I see a choke in your pics which is not used in the schematic you posted. Is the choke in your amp providing power to the whole amp or after the power tube tap?

Stevem, Was your power supply ripple measurement before or after the 1K supply resistor?

If the selector is wired to the OT, then those readings make sense. If so, lift the OT wires and try again.

Smokebreak3 wrote: ↑Thu Aug 21, 2025 11:50 pm
... the other is green. I dismissed it as another CT, but now I have no idea what it is.

It is the ground for the bias winding.

With the current transformer, which most likely came out of one of the 1200 series Univoxs, you can expect to see a voltage in the high 600s. I have seen a few 1200s just over 700V. I attached a U1221 for reference (which eccentrically is what this modified U320 is now). To hit a target of 450V, you...

Japanese Univox (Lafayette) U-320 - designed with a voltage doubler and meant to run 7591's Someone earlier changed the transformer and rewired it for 6L6GC's Owner wants it returned to 7591's The new transformer is putting out 268vac across the secondaries, so running through the voltage doubler g...

half_smith wrote: ↑Sat Jul 26, 2025 5:43 am I've seen mention of this scenario but couldn't find the thread again

https://ampgarage.com/forum/viewtopic.php?t=27035

I use filler rated for exterior use. They also make a two part wood filler. Bondo for wood

syscokid wrote: ↑Mon Jun 30, 2025 7:04 pm
1/2L = 1/2 watt?
1L = 1 watt?
6P = 6watt?

It appears you are correct. I cannot read Japanese but note "1." I believe says 1/4 watt unless otherwise noted.

Those 50L6s need to be wired in series, not parallel. Not sure how you would propose wiring the humdinger but while 500 ohms works for 6.3V, you would smoke 500ohms at 115V. Showing the full arrangement here is important.

it’s not good to run a electrolytic that far under its rated voltage because they will not stay formed and there life will be shortened by some 25%. If you could direct me to some reference material that describes this effect, I would like to learn more about it. I have read a few papers on deratin...

lonote wrote: ↑Fri Apr 18, 2025 4:22 pm

Is that is the same hifi Pioneer?

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Take a look at the the Pioneer SR-101 (attached) for some ideas. Nice sounding circuit.

So, swapping B+ and B++ on the field coil? I know a lot of radios run the Screens off the first node. No. Both the Plate and Screens, and the feed to the next node come off after the FC. I have attached one example of what I am referring to. At the voltages and outputs you will operate at, there sh...