CONN organ tube amp guitar conversion

[Cygnus X1]

Well I've been playing this off and on for a week...it's too loud for me to use.

I imagine it gets great tone dialed up but I just have not been able to do it.

[Ran Randle]

I know what you mean about it being too loud. I added a tone control, replaced a cap to the AT7 preamp tube and got rid of the tone wheel tower thing. It of course sounds much better now an I'm able to get the highs that were really needed.

[Rhodesplyr]

Many Leslie amps have OC3s to set the screen voltage. In the right circuit, they pulse brighter in time with loud transients :-)

[Cygnus X1]

Update...played the life out of this amp to assure the Skip Simmons theory: Sometimes old filter caps are just fine.
She's quiet, no hum, no heat issues.
So bearing in mind that the tone is great but far too loud I took a chance and installed a Fischer Type Master Volume.
(Style 1, with dual 1 Meg pot).
Works, actually works great.
Dialing up one way or the other gives either more potential for preamp distortion or potential clean headroom.
Wrong combination can produce some nasty feedback, but controllable with the guitar V/T controls.
Either one can produce good touch sensitive tones, just different from each other.

I'm satisfied, on to building a head cab for her.
And I'm leaving the filter caps alone.

[Ran Randle]

Update...played the life out of this amp to assure the Skip Simmons theory: Sometimes old filter caps are just fine.
She's quiet, no hum, no heat issues.
So bearing in mind that the tone is great but far too loud I took a chance and installed a Fischer Type Master Volume.
(Style 1, with dual 1 Meg pot).
Works, actually works great.
Dialing up one way or the other gives either more potential for preamp distortion or potential clean headroom.
Wrong combination can produce some nasty feedback, but controllable with the guitar V/T controls.
Either one can produce good touch sensitive tones, just different from each other.

I'm satisfied, on to building a head cab for her.
And I'm leaving the filter caps alone.

Sounds good, glad you got it to your liking. The dual 1M pot sounds interesting.

[Ran Randle]

Conn update

Hey all, I decided to completely rebuild the Conn into a plexi 50 watt clone. Still working out some minor issues (missed some star ground connections )and will post an update soon.

[Cygnus X1]

Sorry I haven't stopped by in a while.
What a change of events Ran!

Good choice, the iron is certainly sufficient to handle it.
I'm still enjoying mine as a "Mega Proluxe"...or something like that.

[Ran Randle]

No problem, this was a huge change indeed. It was very challenging to get everything to fit in the small chassis, yikes. I've redone the board since that last picture and double checked everything. I’m still waiting on a 50k bias pot and a 330uf cap. Then I'll give it a go.

[Ran Randle]

voltage problems

The schematic on the plexi 50 uses 325-0-325 secondary voltages and the Conn PT is more like 340-0-340 so can I add another pair of rectifier diodes to get it where it needs to be like on the bassman 50 amp? I'm considering just making it into a 5F6-A Bassman since that is much closer match for the PT and OT.

[Cygnus X1]

Good work fitting that board in there!
Since you're so close why not go back and use a GZ34/5AR4 to drop the voltages?
I'm still running mine with as I described, still running the old caps.
Made some sound clips too, I have to find them.

http://soundclick.com/share.cfm?id=10067186

[Ran Randle]

Hey, thanks! Your Conn is sounding good! So I went ahead and put in the 5AR4 rec tube but still having issues, p tubes red plating, getting sound but its kinda out of control. I think it may be under bias and/or the choke is too small, only 5H. Need to find a large resistor to substitute the choke perhaps. I really need to double check everything, check out the changes in the album.

[Cygnus X1]

I'd just go ahead and buy a couple 9H chokes, Weber sells them cheap and I haven't had any trouble with them (yet).
Are you still way too high on the B+?
Yes, check everything carefully on your bias circuit.

[Ran Randle]

I need to redo the bias circuit and switch some components to match the JTM50 layout. I made some(JTM50 type) changes and the B+ voltage is lower but one power tubes does start red plating still. I'm getting a shrill squeak sound for a second then nothing. I would have to still get two 32+32 can caps to match specs for the JTM50. Could I still use the 50+50 can caps with no issue I wonder?

Did some research and I think the 5H choke is ok for the JTM50, it originally had a 3H so the larger value= the tighter cleaner the amp would get.

[Talyn]

Really cool to see others have figured this out too.

I went to fix my organ for fun, thought it was a bad cap, found this inside. I cannot wait to actually work on it. It has 2 bad Tubes causing some issues, but works otherwise.

I wish I had a clue what you guys were talking about though in the thread. haha. So confusing to me. Guess I've been outa the loop to long, but then I know not a damn thing about tubes or amplifiers.

[Ran Randle]

Really cool to see others have figured this out too.

I went to fix my organ for fun, thought it was a bad cap, found this inside. I cannot wait to actually work on it. It has 2 bad Tubes causing some issues, but works otherwise.

I wish I had a clue what you guys were talking about though in the thread. haha. So confusing to me. Guess I've been outa the loop to long, but then I know not a damn thing about tubes or amplifiers.

I'm still learning myself, its a lot of fun. That amp looks similar to ones I've seen for sale lately on the bay. Its got some thick dust layers going on there, haha. Looks really cool! Good luck with it, cheers.