Got a real beat-up Twin Reverb...

[greiswig]

Well, I did it: I got one step closer to building a 100W Dumble-ish something. A guy on Craig's list had a chassis (no cabinet) for sale cheap, and it actually works. But man, is it beat up! It's a mid-70's chassis from the looks of it, and from what I can read of the info on the underside, but the last number of the manufacture year is gone. So I can't tell directly what circuit it is. The component mounting boards (don't know what to call them) are warped badly, so they'll need replacing. It looks like I'll have to replace some tube sockets. But as far as I can tell the iron is okay, and the chassis itself is salvageable.

Someone had tried to "blackface" it with a can of Krylon. Sheesh...

Anyway, I have a D'Lite that is pretty heavily modified. I can't decide on whether to try an HRM or not, but I'm open. Using "search" I found that Alan (67Plexi) had said the OT was only good for an "older non-HRM." True? Whyzat?

I do know I would like to try to use one of the extra tubes to put in a built-in D'lator.

Can anyone point me to
- a source for parts like the circuit boards that I'd need for this project
- a source for a head cabinet
- someone's schematic and/or layout of having done a similar conversion, hopefully that keeps a Fendery clean channel?

Thanks muchly, as usual,

-g

[Bob-I]

This guy http://shop.ebay.com/merchant/coastline ... omZQQ_mdoZ builds head cabs for Fender combos for $130. I haven't seen them but he has 100% positive feedback.

As for the circuit, Normster had a layout for a Twin Conversion awhile ago. I don't know if he sill has it or if it's been tested. I make my own eyelet boards with a drill press and a centerpunch. Works great.

Good luck, sounds like a fun project.

[greiswig]

Thanks, Bob. Kinda weird to think about spending as much on the cab as I did on the chassis!

I contacted Norm to see if he still had that layout.

Had you heard anything about why the Twin OT might not be suitable for an HRM?

[tubetek]

The late TwinReverb used an Ultra-Linear OT AND the PT used a Bridge Rectifier setup. If this is the model you have, it's not the best to use for a Dumble clone. The earlier Silverface Twin PT and OT are exactly what HAD used for most ODS builds. Does your OT have 3 or 5 leads on the primary?
5leads indicates the Ultra-Linear setup. Hope this helps...
Tom

[jelle]

IMHO, the UltraLinear OT and the higher voltage PT can sound awesome too. It might not be 100% clone material but it is possible to get an awesome amp with those parts. In case you have UL stuff and you want to part with those, let me know. I'd use it!:D

Jelle

[Bob-I]

I agree with Jelle on this. I've built 2 UL Dumble's with bridge rectifiers. They sound great. Just be careful of the screen voltages.

[jelle]

Or just go UL on them sovtek 5881's. They seem to wake up at those conditions.

Jelle

[thyx]

I've got some UL trannies, but saving the OT for my Boogie MkII. Except for the lack of an 8-ohm tap, it's a direct swap. And the PT is just what the doctor ordered for the B+ on an SSS.

[Stanz]

I did the same thing with an early 70's Quad head. I used Funk's boards. I was not able to mount the two boards (bias and relay supply?) that normal go up against the side of the chassis on the side. Since I had to mount them on the floor of the chassis, that left no room for the PS board. With all of that, I ended up putting the PS filter board under the chassis where the "dog house" is located, leaving the cover off. I added a D'Lator and reverb section as well since it the tubes for it. Reverb is probably a waste of time (for me), but no harm no foul. I just don't use reverb on an amp any more.

I used the HRM 101 schematic, and added in Henry's schematic from his Super Rev conversion for the D'Lator and reverb.

As for keeping the Fender clean side, well, maybe go with an earlier Dumble version that used more typical Fender values (version 124?). I ended up keeping my 70's Twin just for that reason, I wanted the clean Fender sound. Very modified though, first channel can be switched in to add extra gain stage, as well as power scaling, which allows me to drive the power tubes more without blowing out the walls.

All that said, I really do like the non-HRM clean sound. In fact, my non-HRM amp is still my favorite amp in being able to go from clean to modest drive, to heavy sustain, with all stages being very very usable, and the tone remains fairly consistent throughout. Good luck with the build. You have a great platform to build one for sure.

[Structo]

I searched and searched and I found this layout but I don't think it's the one you are talking about.
But it is a neat layout none the less.
https://tubeamparchive.com/viewtopic.ph ... highlight=

[Funkalicousgroove]

The UL isn't the reason those amps sounded crappy stock,

If it were me, I'd use a big resistor, like 10K 20W (just picking an arbitrary value, haven't done the math) to get the screens down under 450 and ditch the UL taps all together, I'd also use a choke before said resistor for nice clean DC, after that the standard dropping strings should work just fine.

Nothing at all wrong with 135W twin Iron-

[greiswig]

Man, I love this group.

[tubetek]

Guess I shoulda been a little clearer; as Funk and others have indicated, the tranny set will work, you just have to re-design the power supply and ignore the UL taps. I guess what I meant to say was that the UL set won't work in the "stock" circuit.
Tom

[Funkalicousgroove]

Actually, the UL can also work, what you need to ditch in that amp is really the piss-poor ground scheme, and clean up the lead dress, which gets rid of the oscillations, so you can get rid of the tone robbing pf caps to ground.

What I think is fun with these is you can have 2 amps in 1 box and use an A/B to select- no relays necessary!

[thyx]

What I think is fun with these is you can have 2 amps in 1 box and use an A/B to select- no relays necessary!

I've always thought that's cool, too...but I realized many years ago that the two sides, unmodified, are out of phase with each other. If you're the kind of guy who pays attention to such things as being in phase with the rest of the band, that doesn't work...unless you put a pedal of some kind that reverses the phase between your A/B box and one of the channels.