Anyone build an 18w Liverpool?

[v00d00blues79]

I'm considering building an 18w version of the Liverpool amp. Anyone try this? I understand that you have to increase the 1k 25w resistor to 1k7/25w, but are there any other considerations? i have some 18w iron that i picked up off of the 18w forum and was thinking that this would work ok for a project of this manner. Thanks in advance for any info anyone might have.

Thanks,

Andy

[Mark]

Dear Andy

The other thing to consider is the current rating of the power transformer. I think you'd want a transformer that would have 250 - 0 250vac secondary, and be rated at 150mA to 200mA.

I say this as I have pretty much exclusively experimented with the 12 to 18 watt Express/Liverpool amps. I found that 260 - 0 -260vac would result in the rail voltage being a bit too high.
I found 250 - 0 -250vac gave me a rail voltage of roughly 335VDC which is what the rail on the 4 X EL-84 amp would have.
I did experiment with a few power transformers and found that this design requires a high current transformer as sag at the output stage did drastically alter the tone of the amp. This being the tone started out quite bright and then as the amp was cranked up the top rolled off in a extreme way.

As far as the cathode resistor in the output stage, try experimenting with anything from 130 ohm to 220 ohm. You may find the amp sounds better with the higher value resistor as the crossover distortion isn't so overwhelming.

That's my two cents Andy, of course I do recommend listening to other opinions, but that's what I have found.

Yours Sincerely

Mark Abbott

[loverocker]

Yes I did one (in a donor test-bed chassis - an old WEM). But I didn't follow the schematic rigorously. I kept the WEM iron, the EZ81 rectifier, and I can't for the life of me remember what I did about that PS resistor

It's on my list of builds to tweak - there were a few issues (where the gain is, tone controls, etc), but there's enough magic in there that it's worth the effort.

[v00d00blues79]

Mark,

What transformer would you recommend? I've looked at the hammond trannies and i only see a 250-0-250 with a rating of 70mA. I have emailed Heyboer and am now waiting on a reply. Also, what would you recommend for an OT?

Thanks,

Andy

[Moose]

Mark,

What transformer would you recommend? I've looked at the hammond trannies and i only see a 250-0-250 with a rating of 70mA. I have emailed Heyboer and am now waiting on a reply. Also, what would you recommend for an OT?

Thanks,

Andy

Why not just use at standard power tranny at 260-0-260 and slap a zener on the centertap to solve the voltage problem? The normal TWPT supplies plenty of juice at 300mA, and you can even switch the zener on the centertap a'la the Blues Express if you want to try higher and lower voltages to see what you like.

And, more to the point, the difference will only be 10-15V on the plates, and you can get almost that much difference by plugging the amp in at a different venue with a few V difference at the wall. In other words, it is probably close enough for government work, even without the zener.

For an output tranny, I've used Graydon's (Heyboer) 18 watt tranny with a liverpool PI and 2xEL84 output and it works fine. S2's trannies are also good, and I would reccomend them as well.
http://www.s2amps.com/transformers.html

MM has a great 18watt tranny, but at $90 or more it's a good deal more expensive than the S2 or GDS transformers, which are of fine quality and only $65 or so. I LOVE MM stuff, but wouldn't reccomend spilling the extra cash in this instance.

-Moose

[Mark]

Dear Andy

Moose's reply sounds good. Try contacting Phil at Heybour and see what he has available. I do recall someone saying he makes a suitable power transformer. I don't know what to say about his 18 watt output transformers as I haven't used them. There should be a few good ones out there. I'm sure the guys at 18watt.com can put you on the right track.

Yours Sincerely

Mark Abbott

[Moose]

Dear Andy

Moose's reply sounds good. Try contacting Phil at Heybour and see what he has available. I do recall someone saying he makes a suitable power transformer.

And don't forget that I still have Heyboer power transformers here from when I bought the huge lot this spring. If you want a stock trainwreck PT, please don't got shopping direct and leave me stuck with this iron, I don't exactly make a big profit on these.

http://Toneslut.com

Obviously, if you want something specifically 250V or of a different size, Phil at heyboer will set you up. Good people to deal with.

[v00d00blues79]

Moose,

as soon as i can scrape some money together and can clear some of the builds off of my bench, i plan on getting a set of trannies from you. I have a 36w, an 18w SIII, and a Carmen knock off in front of everything right now.

Thanks,

Andy