Reducing gain on a 436c

Hi.

I have build a drip's Altec 436. It's sounding great, but I'd like to try it with less of an output before it hits the output transformer. I've built a U-pad to pad it after the transformer and this isn't doing it for me. I'd like to keep my levels going in the same as they are right now. Could I simply put resistors on the "red-white" and "red" ends of the output transformer?

You can't reduce amplifier level without changing side chain control.  An output pad is your best option, and either an H or O pad is your best fixed option, or a Daven type 600/600 ladder or 'T' attenuator. 

Hi. I've put together a U-pad on the output XLR and that works swell enough, but not without (what I hear as, at least) output transformer distortion. I thought it would be nice to check how it would sound by lowering the volts going into the output transformer. Could I put an H pad there then? What kind of resistors/wattage am I looking for? I'm sorry for all these questions, but modifying tube gear is very new to me.

Cheers,
B.

If you built it with variable threshold, you should be able to lower the threshold and increase the output headroom.  Threshold is also ratio.  If it still distorts at lowest ratio, then I would ask what output transformer you used; one capable of handling the audio voltage level?   You cannot pad before the output transformer, that's where the output tube gets it's B+.  

Hi. Yes I thought so. This idea of having B+ and signal on the same wire is still confusing to me, so it's hard to wrap my head around the concept. I have variable threshold and and a variable input attenuator - that certainly helps, but the amount of input attenuation that I have to do (about 20dB) makes me wonder how it would work if the threshold were simply dialled higher and the output gain reduced by, say, 10dB instead. It's still a fancy sounding compressor and I like the demolition I can do to a, say, bass track or a percussion track with it. I'm using Sowter 8650 on the output and 8346 on the input by the way. That's also a bit confusing, as the spec says the output can handle 19volts (+28dBu). So what distorts then, the mu tube?

It may well be the tube - I recall having to test a bunch of 6BC8 to find one with a good match between the two sides. That minimises the nasty thump and grit you get around the onset of compression.

Have a search around the forum - we discussed this at length some years ago when I was putting mine together. My 438c clone is still in regular use after 7 years - but it certainly has it's own character, and is not a gentle beast...

Hi zebra, thanks for replying. I know exactly how thumping sounds, as I have some channelmaster bc8's that thumped like crazy (almost regardless of plate adjust and cathode adjust). The GE one I have in now is really good in that regard. Also, I suppose it's not the tube since it will happen in light or heavy compression, just give it more input and it will distort. That said, I *do* like it a lot as it is, and since it can't be modded for less gain, that's ok, I'll use it as it is. It destroys (or just compresses, depends on how much you attenuate the input) beats and bass something furiously. I'm making a stereo pair, oh dear.. I sure hope there is a market for a "dubstep" or "hardcore" studio lol

That input transformer will give 12 dB+ more input gain than the original, so it's possible you have input problems.  Have you tried it with an input pad? 

Hmm... I have this:
http://dripelectronics.com/sitedocs/altec_manualpt1.pdf
page 35 and on


I have an input attenuator and maybe I'm psychologically inclined to get an output pad, because I have to dig in so much with the input attenuate to get a proper signal going. Seeing that on the drip manual, what do you think I could do, to get what I want, which in this case is some nice, logical interplay between the input and threshold, generating healthy, undistorted signals, unless I want them to be distorted, that is, crank the input attenuator to zero attenuation and have some distortion going on.. not, crank to 80% and have guitar amp sounds getting out?