Need layout & schem for new DIY amp

[MickeyB]

Just picked up some old irons from hammond organs running a pair of 7591's. Does someone know of a layout & schem to make a decent amp out of these? Also with reverb (got a nice tank with them).
Any help would be appreciated. Thanks.
Mick

[Chuck H]

What kind of music do you play and whos tone do you like???

There is other info that will help too. Like, how many and what type of preamp tubes did the amp run? And, what was the speaker impedance for the unit you took the trannys from?

Chuck

[MickeyB]

More info

Yea, that might help. Sorry about that. Heres what I got so far.
Tubes in it are, 2>7591, 2>ECL86/6GW8, 1>EZ81/6CA4, 3>7247, 1>12AU7, 1>5AR4. Still researching the OT impedance. Found the schem for it (Hammond E-100) but no info on the speaker load or OT.
Also have some other misc preamp parts & pieces to use and another amp with 2>7591, with 1 preamp and rect tube socket.
Looking for a clean/blues type thats under 30 watts.
Mick

[Chuck H]

O.K. You have plenty of current available on your 6.3 volt supply. So there's no limitations on how many preamp tubes you can run (good thing). You have a 5v supply so you can run a rectifier tube (also good, esp. for blues).

7591s are good sounding tubes. If you have the originals and they test good you could use them. But unless new reproductions are quality, and I wouldn't know, I might consider changing to a more common output tube. The primary on your OT is probably 6.6k. That should be fine for a pair of 6L6 types.

When I think clean blues, I think BF Fender. The "tweed" sound is good too but it's a matter of tastes.

Reverb is nice for clean blues tone. Didi you salvage the reverb transformer? Trem can be cool too. What kind of features do you want?

Chuck

[MickeyB]

Thanks Chuck, that is what I needed.
Yes the reverb trans is with it.
Been lookin around at the Fenders, thinking Princeton reverb.

http://www.el34world.com/charts/Sche...ERB_AA1164.pdf

This should be compatible?

[Chuck H]

Thats a good one. But there are a couple of things about the PR that could be improved for your needs.

First, the phase inverter is a split load type. They are not typically very good for headroom. So you can't get good volume playing clean.

Second, the trem on that amp uses 1/2 of a 12aXX tube. The better sounding trems use a whole 12aXX (both triodes).

So what to do??? Easy:

http://www.schematicheaven.com/fende...6g16_schem.pdf

I've heard the 6g16 has a very good trem. It also uses a long tailed phase inverter for better headroom. Just omit the "normal" channel and your at 5 preamp tubes. Also, I've tried a suedo similar reverb circuit with limited success, so you may want to use the standard BF type reverb circuit. If your inexperienced you may or may not find it tricky to retrofit the layout. But I think that would be the way to go. Also, If you plan to stick with the 7591s, you may want to change some componant values in the phase inverter. Same layout and schem though, so that's easy.

Chuck

[MickeyB]

I like the look of that 6G16 schem. Thanks.
I wish I had the 7591's but the guy sold them out of the chassis before I could get em.
I like the old 6L6GC's and sure I can find some around.
I sure appreciate your help Chuck.
Thanks again.

[MickeyB]

2 chokes?

The hammond has 2 small chokes side by side together. Do I keep it that way in my chassis? Or buy a new one.

[Chuck H]

Are they parallel or series in the circuit, or are they used on separate B+ rails???

Chuck

[MickeyB]

In series together. The red wires are wire nutted together and one blue wire on one choke to rect tube and blue wire of other choke to cap. They are small, the size of a small reverb tranny. I do not know the henry size or ma of them. Should I leave together?

[Chuck H]

In series together is interesting. I have to assume that either choke would be undersized by itself. But placed in series they share similar properties with resistors in series (ie: you can use two 5 watt Rs in series for a 10 watt application as long as the total resistance is the same and the Rs are of equal value). So I would try to use them as they are wired now. Could just be relative to what the MFG had to build with when this amp was designed. If you want to be sure about the henries (henry's?) you could BUY a standard choke, but since the amp is still basically going to put out the same power it always has, it probably isn't critical. Use them as they are wired now.

Chuck