Champ Build

[Blackburn]

Got an old AlNiCo speaker in today and got to check it out with my Champ build. Really digging it, but it's really, really low output. I used a tweed Princeton OT with 4R, 8R and 16R taps. I originally used the trannies in another chassis where the multiple taps on the OT's secondary served a more significant purpose. They did come in handy, since the Rola speaker is 8R. The B+ is low, at about 305v on the plate. Only thing now is to pop some nice old tubes in there.

David

[Firestorm]

I always found that the efficiency of the speaker was really key with these. Not that you'd use a JBL.

[Structo]

Yep, not all speakers are created equal.

The sensitivity of the speaker (SPL) is key to how well it transforms power.
Or could be the OT.

I repaired a silver face Champ a while back and I plugged it into a V30 and I couldn't believe how loud it got and the drive at top volume.

[ampmike]

Could that amp drive a 10 inch speaker,just curious?Nice build ,thanks for sharing.Mikey J Mercurys too

[Blackburn]

Even with the new ceramic Weber the output was still lower than expected, and that speaker is much more efficient than the Rola. Maybe my EH6V6 is weak? I also biased the second half of the 12AX7 a bit cooler with a 2.7K resistor. I just might pop a 1.5K in there and see just how much more I can get out of it.

[Structo]

What is the bias on the 6V6 (cathode resistor) ?

[Blackburn]

500R is what I have in there. The cathode reads 16.4v, so not particularly hot. The plate is right where I remembered at 305v. The pre seems to check out as well.

[212Mavguy]

The most obvious reasons for low output is combination of too small an OT and the cited too low plate voltage. Tweed Princeton SE OT? Too competent of a builder for much anything else to be the culprit. My Champ type is my first, laughably horrendous looking turret board build, has a 30 watt rated fleabay buzzard swooped secondhand Heyboer single ended OT that dwarfs the oversized PT, had to be mounted in the bottom of the cab w/t-nuts. Using 16 ohm tap to the speaker jack. Board standoffs are carved pieces of Chimay Grande Reserve corks.

It might be period correct, but recreated cheese is still that exact kind of cheese. Not too many folks roll OT's in a build, but on this very first one of mine I used the stock, then a chinese upgrade that weighed more than three times as much, finally the brick arrived in the mail, and the difference between the three diffferent OT's in that circuit was shocking. The 5-7 pound brick keeps up with a full band on stage driving a 16 ohm 2/12 or a 1/15...with a vintage TungSol 6v6, but after a few bottles came in the mail and got listened to with adapters in a '68 Sup Rev I'm gonna rewire the power tube socket and cathode bypass resistor for 5v4 rec'ed 6ar6/6384...The secondhand same cutout PT is an oversized Allen, puts out more voltage in the high windings, so not a fair comparison with OP unit.

Compared to the OP I'm quite ignorant in my ampbuilding knowledge, but this is some of what I did within that ignorance and this thing bellows, howls and screams with vigor of a raped ape.

with utmost respect...

[Blackburn]

Thanks for the compliment, 212Mavguy. I agree that the OT is a big part of it. I prefer my builds with lower voltages and don't plan on changing the PT, so maybe I'll try a different rect and maybe even have a look on Fleabay for a nice old SE OT too.

Interesting adventures in transformerland you've had. The best kinds of experiences part swapping are like you mentioned. Sounds like that amp is a keeper!

[212Mavguy]

Vintage 5v4, 5r4, 5ar4 recs same heater draw as 5y3, pin compatible, 5v4 is indirect heated slower startup like 5ar4, at a fifth of the price and nearly as strong in current with voltage higher than 5y3, closer to 5ar4 levels as well. Tighter louder and brighter than yer 5y3 when dimed.

[dorrisant]

Board standoffs are carved pieces of Chimay Grande Reserve corks.

Lol... Genius! That's what a couple of bottles of that stuff can do... You start to see things differently!

Tony

[Blackburn]

Vintage 5v4, 5r4, 5ar4 recs same heater draw as 5y3, pin compatible, 5v4 is indirect heated slower startup like 5ar4, at a fifth of the price and nearly as strong in current with voltage higher than 5y3, closer to 5ar4 levels as well. Tighter louder and brighter than yer 5y3 when dimed.

I have old specimens of all those rects, so that should allow for plenty of fiddling. I switched the driver half of the 12AX7 to a 1.5K on the cathode and can report earlier breakup and much more classic Champ tone. A 2.7K works better for a darker jazz tone with much less crunch.

[212Mavguy]

Board standoffs are carved pieces of Chimay Grande Reserve corks.

Lol... Genius! That's what a couple of bottles of that stuff can do... You start to see things differently!

Tony

Yep, for a while I ran a wire from pin 3 to a custom jaw bend alligator clip and stuck in an el38 Mullard. Wooooooeeeeee! The blue label can get ya to do things like that...