Sorry for not posting regular. It's been a very busy year, but I do check in daily, if only for a few minutes. I figured that this info may be helpful to someone, for future repair work of this model amp.
I just took delivery of a Guild Model 66-J amp, on Monday (16Dec13). Before I purchased it, I searched for a schematic and found only one original. But, I did find Sluckey's nicely drawn schematic on this site. Tuesday, I put it up on the bench to bring it up on the lamp limiter. I had been forewarned that the fuse block was broken. It's one of those little ones, that holds the glass fuse in two clips, mounted inside on the chassis. One clip was gone. I'm thinking to myself that this is going to be an easy fix. I jumper the two wires together, as my limiter has it's own fuse holder, with a 3 amp fuse installed.
So, it's on the limiter, and by the time I'm up to a 100W bulb, I notice the first resistor in the power supply is starting to get hot. This is definitely not the first time that's happened, because it's a 3 watt resistor and the color bands are cooked beyond reading. I start checking the amp against the schematic (original and Sluckey's), and my amp doesn't match. Mine is a 7 tube, and the schematic is for a 6 tube. The insides of this amp have all the appearances of not being touched, and everything looks original to the amp. I make a quick check of DC voltages throughout the amp, knowing they will be low. I have high voltages where they should be, so I power it down.
Frustrated, I begin the slow process of drawing a schematic from scratch. I decided to make a layout drawing of the whole amp, including the chassis. That way, I can have it on the screen while I'm making a schematic. Between my multimeter and my capacitor tester, I came up with all the values, though a couple are questionable. I indicated those on the drawing, the cooked one being one of those.
All pots are 1M in value, and dated to '57. There is a 12" Jensen dated at '56, and two small speakers (maybe 3" each) paralleled to each other, date not determined on those. Speakers appear to be original to the amp, or at least as old as the amp. The 12" has a DC ohms just a little above 6. The two paralleled have the same. So, each load can be considered as 8 ohms impedance. For now, I'm assuming their connection to be at two different 8 ohm taps.
I completed the schematic, along with the layout. I made the schematic very spread out, to be easy to see, and to go back and make it look a bit better. But for now, it's good to have something to troubleshoot by. The configuration is a departure from what I'm used to seeing. And maybe it's just the way I have it drawn.
As a final step before troubleshooting, I put my auto-transformer on the primary of the OT and connected a meter to the primary and secondary. I eased the voltage up to 30vAC, and saw nothing on the secondary. So, I shut it down and disconnected all. I took DC resistance readings of the primary and secondary. The primary is open. No resistance at all. The secondary has low ohms, but I forget what they were. I've got to purchase a replacement, though this one has four leads on the secondary. One lead was taped back. It's color may originally have been red, but it's too faded to tell. The other three leads are also too faded to tell their color. I'll go back and check the primary again with my Meggar set for 500v. I forgot about it earlier, when I was in the amp. That will prove an open real quick. I'll make resistance readings of the secondary, to have some idea of what I'll need for a replacement.
Anyway, use this drawing as reference, and please note errors, if you see them. I'll make corrections and re-post. Have a good one.
Topic: Guild 66-J Amp.......... (Read 8445 times)