Liverpool Power Tranny

[Buschman]

I recently bought an Ebay tranny. It is old huge iron and I am looking for some input about it. I am pretty sure the ac pair is the black and black with white. When I hook up 120vac I get.

7.2 vac on a big pair of black and black with white wires. Will this come down enough when there is a filiment load on it?

5.8 volts on another heavy pair. I could run a rectifier tube.

598 vac across a green with white and red pair. This group has a white centertap. Looks like a good voltage for el84s.

Do you think it will work?

[bbrunskill]

I'm just getting into this DIY amp thing and found this site. Is the Trainwreck based off a comercial amp? I'm just trying to get a feel for it's sound. I'm halfway though my current project (18watt) and I'm already thinking about the next one . . .

[Ron Worley]

I would characterize it the least commercial of any "production" amp...only about 100 were made, all collector's items worth ~$25K plus....

Ron

[Wayne]

I think the customary response to these type questions is this:

http://www.youtube.com/watch?v=PMAYWeZVjGQ

W

[skyboltone]

I recently bought an Ebay tranny. It is old huge iron and I am looking for some input about it. I am pretty sure the ac pair is the black and black with white. When I hook up 120vac I get.

7.2 vac on a big pair of black and black with white wires. Will this come down enough when there is a filiment load on it?

5.8 volts on another heavy pair. I could run a rectifier tube.

598 vac across a green with white and red pair. This group has a white centertap. Looks like a good voltage for el84s.

Do you think it will work?

That's a pretty strange combination of colors. Filaments are usually green or brown with a striped same color center tap. Rectifier filaments are usually yellow with no center tap. HV leads are normally red with a striped same color or black CT. In any case 418 or so volts DC is pretty stiff for an EL-84 in my experience. Still what is is what is. Foreign transformer I wonder? 50hz? I doubt that the 7.2 will get to an acceptable range without a series resistor. Try a .4 ohm resistor in series with the filament windings. A .2 on the rectifier winding.

The measured plate voltage for the Liverpool is about 320 volts. It's pretty vital to stay close to that for real wreck tone in my estimation. YMMV.

[dartanion]

If it's an older transformer with cloth leads, they may have discolored quite a bit. With that said, I have seen some really odd transformer lead colors before.

So, I would guess this is a 300V HT, so this would be suitable for an Express. The questions here are what is the HT current rating? What are the filament taps rated at?

[Buschman]

It is old cloth leads. Hard to know current ratings but it seems big enough to run a quad of 6550s. Guess I will build it and see how hot it gets. What current rating rating would the heater series resistor need to be. Do I need one on both sides?

[skyboltone]

It is old cloth leads. Hard to know current ratings but it seems big enough to run a quad of 6550s. Guess I will build it and see how hot it gets. What current rating rating would the heater series resistor need to be. Do I need one on both sides?

This is where good ol' ohms law is handy. So let's say you build an express. That's 3 amps for the power tubes and one amp for all three pre tubes. So ohms law says (using the values we know) P(in watts)= I^R. Watts is equal to I times I times R. So 16 X .4 = 6.4 watts. So buy a 10 watt .4 ohm resistor. Or put a 5 watt .2 ohm on each leg of the filament winding. I just pulled the .4 figure out of my hat. It should be awfull close though.

[Buschman]

Thanks sky. Where did you come up with the 418vdc figure? I thought 300v ct off of the pt would put me in the 320-340 vdc range.

[Ron Worley]

I think the customary response to these type questions is this:

http://www.youtube.com/watch?v=PMAYWeZVjGQ

W

EXACTLY!!!

That's what brought me to the party!!

Ron

[Ron Worley]

Double post, the site acts weird sometimes....

[Colossal]

I think the customary response to these type questions is this:

http://www.youtube.com/watch?v=PMAYWeZVjGQ

W

Ahhh...it's always nice to hear it ring! Mmmm Mmmm, that's tasty tone.

[skyboltone]

Thanks sky. Where did you come up with the 418vdc figure? I thought 300v ct off of the pt would put me in the 320-340 vdc range.

Good question. I'm using the solid state rectifier value here of 1.4 times the ac voltage with a capacitor input filter. Using a tube rectifier will yield lesser voltages. I suggest you download the power supply design PSU designer II from here:
http://www.duncanamps.com/software.html

This is a great learning tool and will give you VERY close to real outputs.

[dartanion]

Thanks sky. Where did you come up with the 418vdc figure? I thought 300v ct off of the pt would put me in the 320-340 vdc range.

So, you are generating 300VAC on each side of the transformer using a 120VAC source (your wall outlet). We need DC to operate the tube (save for filaments which can be AC or DC), so we rectify the AC. The calculation for converting VAC to rectified VDC assuming no voltage drop across the rectifier (read SS diodes) is the VAC x 1.404 (or just 1.4). Thus, your PT will give you around 420VDC using SS diodes.

[dartanion]

dp