Downgrading OT

[fdesalvo]

Hi, all. Long time, no post. Hope you've all been well.

I've got a single channel AB763 that I built and have been running for some time. She's running 2 6L6s and the OT is a Heyboer hy018343. She's quite loud and doesn't give up the goods at a reasonable volume, despite some useful mods: PPIMV (which sounds great and is transparent), cathode bias, variable NFB, and mid boost a'la Champ II. Still, I'm starting to think the tone I'm looking for is partly due to OT compression/core saturation.

Would moving to a smaller OT to achieve this? Any considerations? The Alan TO26 looks interesting and the ability to have selectable impedance is important for me, since the chassis sits in a small head shell and has to be able to work with several diff cabinets.

Cheers!

[Justin Thomas]

Hey Frank,

Which particular AB763? I'm thinking switching to JJ 6V6s might be an option, too - they'll take 6L6 voltages. Bias accordingly. One of the main differences between Bassman/Super Reverbs and Bandmaster/Tremolux was a smaller OT on the latter... basically the same amp, but "corners cut" in the OT dept. So Allen's description sounds right to me; whether it will accomplish your goal, who can say? Usually it's a last-resort measure, but it sounds like you're there!

Justin

[fdesalvo]

Hi, JT.

It's essentially a stripped down, single channel Super. She sounds spectacular, but stays clean and tight beyond reasonable levels. I consider those JJ's as 6L6s (no direct exp, just reviews). You're right about last measure heh. About the only think I haven't surfed under the hood is a VVR circuit. Maybe that would make sense.

[Justin Thomas]

Having used my share of JJ 6V6s, they definitely aren't equal to 6L6s. But they do act like a smaller version. Just figuring a used pair might be a cheaper and easier almost-last-resort than an OT... I've only had experience with one VVR circuit, in a commercial amp. Wasn't impressed. Like pretty much every MV I've used, good for taking off a tiny bit of overall volume, but used for much more, bluh. But, don't base it on a sample size of 1 amp. And it WAS in a 2x6V6/EF86 mini-head. Worth looking at - if the parts are cheap, go for it.

Justin

edit: is this tube-rectified, and if so, which kind?

[fdesalvo]

Definitely can't hurt to try them - good call on that. Running an old Russian 5U3C (5U4/Winged C).

[Chuck H]

There's nothing about a standard SR that should preclude overdrive with humbuckers at about 5 on the volume control (with the guitar at full volume, some guys seem to miss this). Yes, it runs high voltages. But in the SR that seems to equate with more gain at the PI resulting in some decent OD levels. For example, SRV did very well with an SR and stock strat PU's getting some grind. I would actually expect a single channel SR build to have MORE gain because it's not saddled by loading from peripheral circuits at the mixing stage. If your amp is too clean there may be a problem with the circuit or the input signal (or the expected amount of gain?). I know you said the amp sounds great and has been running for years, but that doesn't mean that it's "correct" or that the input signal is correct or that your expectations are correct.

... Do you have an O scope, signal generator and a dummy load?

[fdesalvo]

Hey, Chuck

I wish I could gig at 5 on the dial. I have the mixing stage set up to simulate the missing vib/intensity pot. Maybe over loaded. I can lift the ground there to see what a boost in gain would sound like. Could make a usable feature on a switch or trimmer. You're right - working doesn't mean optimal.

Wish I had some fun toys at my disposal, but would make sense to invest. I'm kind of stabbing in the dark with some of my tweaking.

[fdesalvo]

Solved: ClassicTone 40-18006. Remarkable difference in tone and feel. The Heyboer that was in there prior was so cold and sterile by comparison. This OT sounds and feels like a proper guitar OT.

[Chuck H]

Solved: ClassicTone 40-18006. Remarkable difference in tone and feel. The Heyboer that was in there prior was so cold and sterile by comparison. This OT sounds and feels like a proper guitar OT.

Funny you say that. I have an amp model that I've built with two different OT's. The proto is built with a stock Hammond "off the shelf" transformer and the later units were slated for a proprietary Heyboer unit. I like the tone of the Hammond better and it's not even a "guitar amp" transformer. Nothing against Heyboer. Those amps sound good too. But my experience sort of matches yours.

[fdesalvo]

I've never had a bad exp with Hammond - even the generics have great tone.