Recent content by jmccanna

Hi, I have two DC300a amps. The second one I got yesterday off of CL from a guy who said it was acting up. Paid twenty bucks. One of the pots was loose so I took off the faceplate to tighten it down and noticed that this one has the IOC lights whereas my first one does not. There is a white...

Hello J, I will be diving into this little puppy in the next week or two. I have an old Akai M8 tube amp I am converting to a guitar amp first. Nearly done there. I imagine I will have struggles finding the right transistors and such. A while ago I repaired a Nikko NA-850 that gave me a run...

James here: I just acquired a KA-3500 off of craigslist from a guy who said it worked fine. He was selling a package deal with the amp, a tuner and some speakers. He said the speakers (which I did not really want) were a bit scratchy. Well, it was the amp, I am getting distortion out of both...

Hello all, I am still working on some final stuff. I cut the original box down to size, cut off the top where the speaker screen was and re-purposed it as the top and glued it on the top. The box had an ugly grey thin stock woven fabric glued to the exterior of it. The paint I used is a...

At last, I found some time to dig in. It was a bad SW1 switch. I finally put it on an oscilloscope and traced the signal path. It stopped at the OT output. The only thing between that and the speaker out was the switch. I bypassed the switch and it works and sounds great. Thanks all for your...

Thanks RWood. I have been carefully comparing the good channel to the bad one and am finding no discrepancies in wiring. I have switched all tubes from the good channel to the bad one and it makes no difference. In following the the troubleshooting guide included in the service manual one...

Hi, I apparently have two schematics for the Akai that are largely similar. One has voltages for the left amp in a couple of places. Using that, I get 119v at the plate for the 12AD7 just before C9 instead of 100v. I get 219v on the far side of R13 (250k). I get 146v off of the second plate...

Well, I changed out the 50k resistor for a 100k resistor and it made no difference. Amp is low-volume, distorted at output. However, it is clean if I tap into the preamp out and go to the other line in on the working amp. I am missing something for sure. Bummed in the NW. James

In going through point to point comparing the full-functioning right-side amp with the partial-functioning amp I noted that R15 differs. In the working amp it has a 100k fixed resistor and in the bad amp a 50k resistor. The schematic calls for 50k but here the 100k amp is the one working.

Thanks so much. Your schematic differs from the one I have. The value of C9 = .01, Cathode cap is C10, cathode resistor is R12, R11=500k. On the second side of the the 12A R16 is cathode resistor at 3K and C12 is the cathode cap. C9 and R13 connect (R13 is 250k). So it is largely similar...

Hi, previously I did check all voltages to all pins and am getting about 1v at the cathodes for the 12A and 7.8 at the cathode for the power amp.

Hello, I have been steadily working through the right side amp of this set and having considerable difficulty. After having figured out the OT was defective I traded for some new ones that tested good. I have gone through the entire schematic and checked all of the components in the signal...

Yep, figured that out when I tried it. The amp worked but the meter went all wonky. I do not understand why but it is clear now. I put the .01 back in and it all is fine now. The amp sounds good so I may as well just enjoy it and start working on the others. Thanks.

Nice work! I am thinking of resawing some figured maple from a great big tree that fell on our house 2 years ago for the case. Question for the group: I am going through the caps on these and all I have for the coupling caps are .15/600v orange drops (schematic = .01uf/400v/600v). I think...

Hello All, Thanks for you insight and helpfulness! After studying the schematic, figuring out tube topology/symbols I managed to identify and replace the preamp cathode bypass capacitor and several coupling capacitors from leftover items I had in my excess bin. That, plus the new OT I traded...