Twin Conn Organ 7868 Rebuild

[rmyauck]

Schematic -wrong one got posted.

Extra wires on primary are for UL taps.

Hammond 1650R 5K 100W (not the easywire RA version either) would be the better one to use as you would get a bigger bandwidth and less distortion.

It is highly liked sonically if you search the forums also.

 

[vrusso123]

Hi rmyauck! thanks for responding so quickly. I only have 3 3/8" between the tubes where the original OPT's are (one is underneath). and 4 3/8" deep. If I remove the Oa3, the 6dn7 (not being used anymore), and re rout the speaker outputs I can put a second one there. Space on this chassis is limited. this is why I am trying to keep these stereo, and hoping that they can be paralleled for mono use if I am inclined. the 1650r wont fit. Too BIG! thanks again for reading and responding!

 

[vrusso123]

sorry bout the schematic. here are the other two pages, might as well post them all. THANK YOU SO MUCH FOR YOUR HELP!!!!!

 

[rmyauck]

Maybe just leave those amps original (use in another part of your house/office) as you got them working nice and just start new using the 1650R and a diy chassis if you want more power. You can get a nice 50-60W/CH with only 2 KT-88/KT-120 per channel for much greater simplicity/possibly sonics and a better chance of success.

Here is a great design you could do easily P2P (wired point to point) or with PCB's if you want them.

http://www.diyaudio.com/forums/tubes-valves/158322-my-kt88-williamson-amp-build.html




You can never have too many tube amps!

 

[vrusso123]

I could move the output tubes to the back row, (caps and sockets unused) which would give me room for anything I want put on it, but my knowledge and skills are EXTREMELY limited and I don't want to turn these to junk, as I have with other projects.

 

[vrusso123]

my original thinking in this was to use these amps to start learning about tube amplifiers . I never really expected them to be good amps. Then after all I have read, I realized these could actually be the only ones I would ever need. that with some decent OPT's these could really be some badass amps. Being new to tubes, these are really hard decisions to make for me. Knowing if the parallel OPT's are really putting out twice the watts is the deciding factor I guess. if that option works I would like to go 2 channel on each amp. if not, they will be mono block PPP. Any ideas?

also.. I would like to be able to use one while working on the other, then when both are finished, use them any of many, many ways.

 

[vrusso123]

I think I can shoe horn a pair of the edcor CXPP45-MS-6.6K in there. by the way, am I correct about the 6.6k primary for a pair of these tubes?

 

[kevinkr]

Thread renamed per OP request

 

[vrusso123]

Thank you. your site and members are awesome. This is all new to me, I didn't know recorded music could be this good, and I have this forum to thank for that.

 

[kevinkr]

 

[vrusso123]

soo... I'm running them with the OPT's secondary's paralleled from the 8 ohm taps (4 ohm).Cleaned the contacts on all the tubes with deoxit, removed the "gain" pots, and added RCA inputs where the pots were.

I have to say these things are whales. they really have some serious slam to get these Logans' moving as they do. At low levels the detail and depth are amazing. Cymbals still sound subdued and distant. I could probably live with this, but why? I can just fit a pair of Hammond 1650p's on each one. I'm going to order a set as soon as someone here says go, cause I don't know what I'm doing, and I'm gonna need just maybe a little help. circuit mod suggestions would be awesome too. I have to ask, is it safe to parallel the OPT's? they sure seem to be more dynamic, and a little louder, but I have nothing but my ears to judge.

 

[vrusso123]

here is a pic of a cool speaker my friend found mounted in the ceiling of a porch he was tearing apart the other day. thought you might like it.

 

[vrusso123]

hey all! thought I would give an update. Well, I was pretty sure I was missing high frequencies above 12k with these amps. I bought an old Maggie console with 6bq5's in it, and after a recap and a good testing 6ca4, my suspicions are confirmed. The little Maggie has way better highs although not much volume before breaking up. I suspect 3w is not enough power for martin logan aerius I's , although it is loud enough for listening at moderate levels. I bought these Eico st-70 output transformers last night from fleabay, along with some ceramic sockets, speaker binding posts, and rca inputs, and plan on putting the first one together when the parts come.

thanks again for your input, much appreciated! The plan is to make a pair of 2 channel amps with these, using old Eico iron.

 

[vrusso123]

wow. these are huge.

I am going to have to move some sockets around on this so everything fits. I want to switch this amp to 7591a's. can someone make me a pin to pin diagram to do this? I looked I swear.

 

[vrusso123]

any recommendation of socket supplier?

 

[vrusso123]

well, I added the Eico's and had a professional rewire it for me. it sounds ok. the negative feedback was removed, and it sounds hot and harsh. so I put the 18k resistor paralleled with the .0001 cap back in and it squeals. any suggestions? can I make a variable NFB circuit so I can tweak it?

 

[vrusso123]

Awesome. Thanks for all the help.........

 

[vrusso123]

although nobody seems very interested, I am going to finish this thread.

regarding the squeal, the primary leads were reversed on the OPT's, hence the squeal.

regarding the negative feedback, put it back to the 18k resistor and .0001 capacitor.
This really quieted the amp down, also balanced it out tonally. It still seemed a little flat (dimensionally) to me though, and I was a little disappointed. last night pretty late I was listening to some ELO and I could hear it change. Sounds got thicker and thicker until it sounded like there were speakers all around me. I had forgotten that there was a new set of capacitors that needed to break in!!!! AWESOME!!!!! So open and extended now.

so the first amp is finished, running 7868's, and sounding absolutely fabulous. here are a few pics, including the up-skirt.

 

[tizman]

Hi. Thanks for the posts. They have been very helpful in my rebuilding of the exact same amp from a Conn organ.

 

[tizman]

I didn't have the .0001 capacitor in parallel with 18k resistor as part of the feedback network in my schematic. When I put the feedback network back together as part of my rebuild of the amp, it caused a loud buzzing when I put just the 18k resistor in. I am going to try it as shown in the schematic in this thread to see if it will work properly this way, and hopefully if it does it will help eliminate some residual hum that I still have. Thanks again.