vintage organ amp to guitar amp HELP

[RWood]

Well, then I refer back to my original post:

you can certainly try it with the given circuit and listen to the results. RWood

I don't usually quote myself, or refer to RWood in the third person, but I am a big proponent of empirical evidence.

[jcart]

conn amp

i was looking at the schematic that I have and there is one tube that doesnt match my amp, this isa 6J5. On my chassis it is clearly marked RJ6 next to a tube socket, Can these tubes be interchanged?...I cant find anything online about the RJ6. Also on the schematic there doesnt seem to be any inputs marked. I am thinkin maybe this isnt my amp?

[chris mckenna]

i was looking at the schematic that I have and there is one tube that doesnt match my amp, this isa 6J5. On my chassis it is clearly marked RJ6 next to a tube socket, Can these tubes be interchanged?...I cant find anything online about the RJ6. Also on the schematic there doesnt seem to be any inputs marked. I am thinkin maybe this isnt my amp?

JC,

Show a picture of the tube. It may have some indication of what's in their now and, are you sure it's a RJ6 and not a 6J6? Is there a tube chart or silk screen on top of the amp?

EDIT: I see it now in the pic you sent to me- it's on the top of the chassis near that tube.

I have checked into the x-reference charts here and, there's nothing other than a 6C5 / 6C4 or 7A4 that is a suitable replacement for a 6J5 driver.

Now, the question is: which amp do you have? The schematic that you sent me states 6J5 but, your saying it's a RJ6 which, I note that now on the amp. I'll bet it's the later tube- 7A4.

Let's get a view of the driver that's in it now. Remove it, take some pics and let's see what we've got. If it's got 7-pins, it's most likely a 6J5 type or 6C4 or 6C5. If it's a hard CAN type, it will be black metal and, most likely, will be the old 6J5 and have an eight pin base with two removed thus having only six pins. Let's see the pinout view as well just to be sure. EDIT: I see now that it's an RCA that's in there now and not the old CAN type. So, that rules that out.

If this amp was made in the 50s, there's a good chance that it was the successor tube to the 6J5 which is the 7A4 and is glass and has the full eight-pin base and is about the same diameter as the 6SN7.

Check that out and let's have a look at what we've got.

CM

[Rhodesplyr]

Just out of curiosity, are there any manufacturer codes on the output transformer?

David

[chris mckenna]

JC,

Your amp is a tad bit different than the models that sport a 6C4 so, we can rule that out as well. [IMG][/IMG]

[IMG][/IMG]

Note the change in not only driver tube type and layout, but, take note of the different phase inverter and the additional tube in the rear which is an OA2- a voltage regulator along with the change to a 12AU7.

[IMG][/IMG]

This is your amp here.

Looks like there's a few different variations on the design and layout of the driver tube. Judging by the OD of that driver tube that's in yours, it looks like a 7A4 which was the replacement for the 6J5.
CM

[jcart]

conn amp

on the OT the stamped numbers read R48531

[jcart]

conn amp.

holy moly!..somebody drugged my oatmeal!!!...after spending hours looking online for a RJ6 tube and finding nothing ..I go back and look at the amp for something else..and there it is...a 6J5...very clearly inked...DOUGH!!!

[chris mckenna]

holy moly!..somebody drugged my oatmeal!!!...after spending hours looking online for a RJ6 tube and finding nothing ..I go back and look at the amp for something else..and there it is...a 6J5...very clearly inked...DOUGH!!!

God help you if that happens when rewiring this amp......oh dear. I hear a Cheech and Chong movie playing - Up in Smoke! HAHAHAHA

[ThermionicScott]

7A4 is a loctal-base tube. You'd know if it had one of those.

This might be irrelevant, but 6L5 is a pretty close sub for the 6J5.

- Scott

[doctorfixit]

Pre-amping the 48425

Chris I have a Conn 48425, looks exactly like the last picture. 2-6L6, 6SN7gt, 6J5 driver, I went to the trouble of drawing this schematic before I found this thread. Dough!! (no representation of accuracy) I want to add a preamp tube to this chassis, possibly replacing the input pot, as there is little room. Any suggestions?

[ThermionicScott]

If more gain is what you seek, consider reworking the first stage for a 6SF5 or 6SQ7. By juggling a couple resistors, you could swap in a higher-mu 6SL7 for the phase inverter. Heck, replace the 6J5 with a 6SL7 and you can add a gain stage without needing more sockets.

- Scott

[chris mckenna]

The thing is, by adding a preamp tube, this means your going to have to design a preamp section / circuit for the tube choice and, there's also another issue that your going to have to deal with if you were do go that route and that is how your going to isolate the preamp CKT from EMI and other noise radiating components in the power amp.

This is why you see most power amps as just that- stand alone power amps. There's no room for a preamp and, there's no room in a small box to get away from the noise. So, what you'll end up with is noise migrating into the preamp section. This is of course, if it's not laid out properly. With a low gain preamp, you may be able to get away with it but, in that small of a space and, noting where the tranny is located in relationship to where you want to put the tube- it's not going to work. The EMI coming off the tranny is going to be an issue.

What I recommend is to design a nice little preamp using 12AU7s (low gain but clean and smooth) and use that as the preamp into the Conn Organ power amp.

But, this depends on your application as to just what type of preamp tubes and CKT design your talking about as, there's quite a few types out there to choose from and, a few different topologies as well. What is the application?

CM

[doctorfixit]

Thank you both for responding. I want to use this amp for a bass guitar. I have done conversions from Hammond power amps that use EL84s , adding a shielded 12ax7 for the preamp , but the 6L6s are better than the EL84s for bass and this Conn is a nice candidate. That 6SL7 idea is intriguing. I'm not opposed to a separate preamp but if I can avoid it so much the better.

[chris mckenna]

No problem. I have one of these coming in to my shop for a total rewire. I believe it's a low wattage amp thus not much in terms of being a bass amp for, bass will drive it into clipping fairly easily I would imagine. What is the rated output before clipping on these things?

CM

[doctorfixit]

Conn 48425 Conversion

I do not know, I would assume similar to the 18W Hammonds? It won't be used in onstage performance.