vintage organ amp to guitar amp HELP

[jcart]

I have a 1952 conn organ amp.(model connsonata ) amp has two 6l6's.. i wanted to use this as a power amp for a guitar setup. anyone here have any knowledge as to where i can get a wiring diagram. or do you think it would be relatively easy for someone to mod this amp such as gounded ac line in, on off switch, maybe newer components?

[RWood]

That looks like a great chassis, tube component and transformer set.

You say you want a power amp only.....no preamp?

The relative ease of doing this depends on your level of experience. Are you looking to plug 'n play, once you put the grounded power cord and power switch in? If that's the case you can certainly try it with the given circuit and listen to the results. You can also take some measurements with the tubes under full load and see how your power suply is performing, measure the B+.

I suspect, though, that what you'll wind up doing is gutting the existing electronics, rebuilding a known, proven guitar circuit in it, but using the existing hardware.

RWood

[JHow]

...where i can get a wiring diagram...

Dang, it looks so clean, I'd be judicious about "gutting".

Someone may locate a schematic for you, but if not, this looks fairly simple that you might want to try and trace the schematic for yourself. This is actually a good exercise, and you can learn a lot by doing so.

Then when you do find the schematic, you can see how well you parsed it out.

[jcart]

conn power amp

i want to use my little fender champ amps line out into the conn...so using the fender as a preamp...i would have someone else do the measuring as i dont want to get fried....i know just enough to get into trouble if you know what i mean.....i could do the power cord i guess...but ill let the cap bleeding etc to others...

[JHow]

Discharging caps is not especially difficult and does not require specialized equipment, however, better not to fool with it if you don't understand it.

No offense (no one here was born with electronic knowledge - everyone has to learn - learning only stops when you die), but how were you planning to convert this amp if you don't have some electronic knowledge? Is someone going to help you work on it?

[jcart]

conn amp

there is an amp shop nearby..he does pretty good work but he is SSSSSSLLLLLLLLOOOOOOOWWWWWWWW. I can do the power cord..do the switch off one leg of that. caps run to ground with(or not) a resistor using a nonmetallic probe..i just cant do any testing..i respect the amount of voltages running around in there so Ill play it safe ..untill i can learn how to...I would like to know if there are better transformers or better quality caps than i have now so as to replace them..that would be good for a start..

[JHow]

...I would like to know if there are better transformers or better quality caps than i have now so as to replace them..that would be good for a start..

Actually, for a piece of gear from the 50's, your transformers look in great shape - clean, not rusty, no evidence of over-heating that I could see from the picture. Chances are very good they work and, whatever they are, they orginally ran two 6L6s, so you should be fine power-wise. Transformers are one of the more expensive items in an amp, so personally, if these work, I would say use them and save my dollars for a good speaker.

As to caps, the only ones likely to give you trouble are the electrolytics (power supply filters). In that case its not so much getting "better" caps, as getting "new" ones. Even (or especially) if not used, they can dry out and not hold a charge, leading to hum. Sometimes they can be "re-formed" by charging up slowy on a variac, but many times they just get replaced. The modern cap replacements will also be physically smaller, which is useful, since you can sometimes hide them under the chassis and leave the original cans in place. You can also get replacement cans, but the question there again are the physical dimensions - do they fit the hole in your chassis, do they fit the clamp.

If you re-build this as a new circuit, or if you trace the circuit and end up modifying the existing circuit, you may end up tweaking coupling caps and the like to acheive some desired tone or design goal.

[RWood]

If you want to give it a shot, I've got an idea for you. Your pictures are good but not great, but here's what I can see.

Looking at the underside, the tube to the left of the 6L6 power tubes is the phase splitter. It appears to be a 6SN7. Please confirm this.

To use the power amp only, you will need to send your signal to this tube, which splits it into complementary signals that are sent to the power tubes. Your rectifier provides the the high DC voltage, so that leaves only the input tube, the one to the far left, center high, unused.

As it is wired now, your input goes to a volume control and then to the grid of the input tube. It is a yellow wire -see it? In the attached drawing you will see my suggestion of sending this signal not to the input tube but to the grid of the phase splitter. Just follow the arrows, do your soldering with the amp good and drained.

You are correct to be wary - there are some bare high voltage wires in there, but if you do lots of reading on safety practices and use common sense you can at least try it out. As JHow said, we all started somewhere.

Btw, I have worked with several Conn amps and getting schematics is not impossible but it's also not cheap - you can buy service manuals for around $20 that contain schematics. Not worth it in my opinion, but an organ parts supply house might have your model if you want it badly enough. Drawing it out yourself though, as was pointed out, would be an invaluable exercise.

RWood

[jcart]

conn amp

yes that is what the tube is..i found a pic of a pair of amps that someone was selling for $400 online that were rebuilt. i saved the pic but didnt save anything else. I would like to find the ad again to get in touch with the person as they were the same amps that i have.
I was told that this might be a self bleeding amp? when off caps will self drain..is this true ? my gut says bleed off everything manually anyways...
I want to install 1/4 phone jacks for the in and outputs . For the in i am thinking just change the connectors ,for the outs I would have to disassemble the connector there... and run the appropriate wires to the hots of each 1/4 phone using the common line for all....i have a schematic but am not sure yet if this is for my amp...any help verifying that it is would be greatly appreciated....

[jcart]

conn amp

here is the schematic i have...hope you can help..this was found online but like i said i am not sure if it is for my amp

[jcart]

conn amp

if the input goes to a volume control..couldnt i use that as a master and leave the amp the way it is?...also what would be the difference if left origional versus your mod?
i was told that the ohm changing dial is similar to certain Marshall amps and they have been known to fault and blow up amps due to no load...thats another reason I want 1/4 phone out jacks. can you tell if the schematic is my amp?...so i can use it to installl the output jacks?

[RWood]

For your speaker jack, yes, use a 1/4" islolated jack. I would use three of them, actually, one for each of the OT secondaries you have: 4, 8 and 16Ω. That way you can use the amp with any one of several different speaker choices.

Before you disconnect the OT secondaries from that connector plug (or switch), note which pin they come from so you can identifiy which is which, from your schematic (pin 1 is 4Ω, pin 2 is 8Ω, etc). Then run your hot leads (probably green, orange, yellow) each to the hot terminal of its speaker jack.

Connect the black (ground) to each of the jacks' common (shield) leads, then run a wire from the last one to where the R5 (off pin 6 of the 6SN7) is grounded. This should be the only place the jacks connect to ground, not the chassis.

Re the schematic, yes, that appears to be correct. Nice find.

You can try the amp as-is, like I said in my first post, where your guitar signal goes through a volume control, the preamp tube, the phase splitter and then the power tubes. Give it a try.

If you are running a signal that is already preamplified, as you then described, it is like plugging that into the input of a guitar amp. Too much gain, difficult to control, probably oscillations etc, but hey, you probably won't kill anyone in the process and it is legal in most states.

My suggestion, moving one wire, injects the preamp'd signal into the phase splitter, bypassing the input tube, the way a proper amp would do it. And you have that volume control already in place. This will be a more manageable and stable circuit IF you are using an outboard preamp.

Btw, now that you have the schem...do you see the capacitor C1 (.01 400V) that goes to pin 4 of the 6SN7? If you do this mod, bypassing the input tube, you'll also want to clip that cap out of the circuit. It won't be needed.


RWood

ps Per your schematic, yes, there is a bleeder resistor to ground so your caps should discharge pretty well. This is where I like to use my ($2.99) meter with gator clips on the ends, connect the black to ground and the red to the high voltage at the first cap, and actually watch on the meter how quickly it really does discharge.

[jrcstudios]

Jcart,
Thanks for your reply on my thread. What I didn't tell you was that I have a pair of these that are the larger model (4 6L6 tubes and two rectifiers)

After re-capping them, I ran a line level signal to the input AS IS with no mods to the amp and use them as a stereo amp in my studio. I have the screwdriver level control about half way and have plenty of gain without distortion. These amps are very Clean, no hiss or hum at all!

Bypassing the Preamp tube as RWood was telling you to do may not be necessary, and you may find that the flexibility of having the level control on the amp is worth leaving it in, so you can match the level of your Fender's line-out to the gain of the Conn. However, if you are a puritist, doing as RWood said will eliminate an un-necessary secondary preamp stage. If you are not comfortable messing around in there, try it this way first.

--JRC

[chris mckenna]

Yes, running line level will work and, as stated above- it will not be an issue. Most power amps use a driver tube and, I believe after looking at the schematic for this amp it's not a preamp tube but a 6J5 which, is used as in the driver circuit to drive the phase inverter.

There's usually no issues when running in this mode and, there's no chance of oscillation or excessive gain. I have been doing this for years on my guitar rig.

I tap all my guitar heads (even 100W plexi Marshalls). It works just fine into tube power amps and, it will work with this one too. On tube power amps, the little tubes (in this case it's a 6J5) are not preamp tubes but rather a driver so, there's no chance of a gain mismatch that is going to cause oscillation. In fact, it would not oscillate but, rather be very noisy and, you'd most likely blow the input section of the preamp (if there were one) as well as the driver section and the first power tube more so than having uncontrollable gain or oscillation condition. From my reading, the preamp was a separate component in the organ.

All you need to do is to simply change the jack type to accept 1/4 and, as stated above, you can also take each tap off the tranny and run them to each jack along with using the common (black wire) to connect all the grounds to each jack. Use isolated jacks on the rear and you'll be all set to go.

If the OHM selector switch shows low resistance and good conductivity, in my opinion, there's no need to add jacks in the rear. The only time I recommend doing that is if the switch itself has corroded over the years and is making intermittent contact or shows high resistance on the pins. I would also get a can of DeOxit and clean it and then check it out afterwards. If it measures up fine and it works, I recommend to leave it alone. However, if you really want to add three jacks for the respective taps off the OT tranny- that's totally up to you.

CM

[chris mckenna]

For your speaker jack, yes, use a 1/4" islolated jack. I would use three of them, actually, one for each of the OT secondaries you have: 4, 8 and 16Ω. That way you can use the amp with any one of several different speaker choices.

Before you disconnect the OT secondaries from that connector plug (or switch), note which pin they come from so you can identifiy which is which, from your schematic (pin 1 is 4Ω, pin 2 is 8Ω, etc). Then run your hot leads (probably green, orange, yellow) each to the hot terminal of its speaker jack.

Connect the black (ground) to each of the jacks' common (shield) leads, then run a wire from the last one to where the R5 (off pin 6 of the 6SN7) is grounded. This should be the only place the jacks connect to ground, not the chassis.

Re the schematic, yes, that appears to be correct. Nice find.

You can try the amp as-is, like I said in my first post, where your guitar signal goes through a volume control, the preamp tube, the phase splitter and then the power tubes. Give it a try.

If you are running a signal that is already preamplified, as you then described, it is like plugging that into the input of a guitar amp. Too much gain, difficult to control, probably oscillations etc, but hey, you probably won't kill anyone in the process and it is legal in most states.

My suggestion, moving one wire, injects the preamp'd signal into the phase splitter, bypassing the input tube, the way a proper amp would do it. And you have that volume control already in place. This will be a more manageable and stable circuit IF you are using an outboard preamp.

Btw, now that you have the schem...do you see the capacitor C1 (.01 400V) that goes to pin 4 of the 6SN7? If you do this mod, bypassing the input tube, you'll also want to clip that cap out of the circuit. It won't be needed.


RWood

ps Per your schematic, yes, there is a bleeder resistor to ground so your caps should discharge pretty well. This is where I like to use my ($2.99) meter with gator clips on the ends, connect the black to ground and the red to the high voltage at the first cap, and actually watch on the meter how quickly it really does discharge.

Bypassing the driver tube will produce hardly any output at all and, I don't recommend that mod. In this case, the preamp was a separate component and, this in turn, took the low level signal up to line level where, it was then fed to this power amp.

This amp does not have a preamp so, in order to reach intended output rating, I recommend using it as is. By bypassing the driver section, the output will be very low.
CM