Pacific Transformers from Reverb.com

[Jay Omega]

I made an impulse purchase of the Pacific PAM-PT-30-54R and PAM-OT-30-54R, and now I'm embarking on my first Trainwreck build journey. I didn't look very closely before purchasing and now I have a couple concerns.

The OT shows 7.5k primary, which looks a bit high. I'm not terribly worried about this as I have a ClassicTone 40-18064 laying around that will fit in the same mounting holes and I could compare them.

The PT spec sheet is confusing. HV winding shows 350V next to the center tap, and there is a note next to the winding that could be read as 560 VCT @ 100 mA. It could be read that you can expect 350 VDC at 100 mA. My only hope is they intended the secondary measured 560 VAC at a 100 mA DC idle current, 100 mA idle current seems reasonable for the amp. If the HV winding is rated for 100 mA AC RMS, just idling should burn it up. Planning to report back with my findings on the PAM-PT-30-54R as I couldn't find much documented on the internet. If I don't think I'm getting enough power from the HV winding I'll pick up a Hammond 272JX which would probably be a touch more voltage than the originals.

Anyone had a successful build with the PAM-PT-30-54R and PAM-OT-30-54R?

[wpaulvogel]

The 272JX works perfectly in an Express.

[Mark]

This might help.

https://www.tube-town.net/ttstore/tt-tr ... anguage=en

https://ampgarage.com/forum/download/file.php?id=6629

[Jay Omega]

Thanks for sharing Mark, I love the voltage chart! Great info in there so I know what to shoot for.

Unfortunately the tube-town PT shipping cost is prohibitive where I'm located, but I did order a 272JX over the weekend so it looks like I'll be making two Expresses. In another thread a member reported that Pacific acknowledged that the PAM-PT-30-54R HV winding is indeed only rated at 100 mA. A bit of a bummer but I could always load that one with 6V6s and save the EL34s for the 272JX.

Once I get the Pacific unit built, I will report back so others will know what to expect voltage and power wise.

[Jay Omega]

Got the amp wired up last night, it’s pretty dang loud LOL. I have the output tube biased on the coldest setting, and was using it with a Two Notes Torpedo Captor with a cab on the -20 dB port. Sounds pretty unique I’d say, it does really good with high gain. I wasn’t expecting to be able to get metal sounds out of it, and playing an 8 string guitar sounded surprisingly tight on the low end if you dial it in right. I have some oscillation in the preamp, going to start chasing that tonight.

I’ll bias the power tubes tonight and see what kind of clean power I can get with a resistive load. You can definitely hear the power supply breathing in this amp when you chug, it’s pretty slow to recover, unsure if that is related to the skimpy HV winding yet

[Jay Omega]

Alrighty, so I did a bit of work tonight - reduced the preamp oscillations and did the power test. I'll say this amp was trickier to tame than I expected considering it only has three gain stages, I wouldn't recommend beginners attempt to build unless they have a known working layout and some lead dress instructions as a guide.

I first biased the power tubes, they're TAD EL34-STR REDBASE. Mine are matched and labeled PC 35 and TC 1067 which I'll guess means plate current and transconductance. The data sheet says they're rated for 25 W, I biased them around 70% plate dissipation which required a bias voltage around -35 V. At plate current around 40 mA per tube, power transformer put up a plate voltage of 410 V.

For the power test, I fed a 1 kHz sine into the cold clipper grid. I had an 8 ohm resistive load connected to the amp, presence control was on zero, and the negative feedback dropper was the stock 100k. The amp put out 20 W cleanly without issue, had some decent compression around 30 W, and the onset of heavy clipping was around 40 W.

Thought I'd put it out there for anyone looking at using the Pacific transformers they're selling on Reverb.com. The amp sounds pretty good, but I've never played a real Trainwreck or a clone before.

[Mark]

I would have thought that you would have gotten more than 20 watts out of it. I have yet to build mine so I can’t say what is normal.

[Jay Omega]

The test was somewhat subjective, I adjusted the function generator amplitude while looking at the output voltage. I could throw it on the distortion analyzer if interested, to see what kind of output we get at 1, 5, 10% THD for example