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Spec 2 Salvaged

OK. I'm setting up the DBT and about to put some power to this beast....Get your popcorn ready....IMG_20191206_164329763.jpg
 
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So far so good. 150 watt bulb went out, 75 watt bulb went dim. Not out of protection yet. Put on house power but still in protection. Also, both meters jump up to about 0.05 watt. Gonna check bias now....
 
EastPoint said:
Is it still in protection?
Click to expand...
Yes it is. Doing some testing I have 86v on pins 19,20,21 on the power supply. Manual says 91v but I guess 86v is close enough, However, I get 1.98v on pins 23,24,25 and the manual says -91v. I think I'm on to something.....
 
Got it. Loose fuse connection @ FU-2 on the power supply board. Also, one side of the xformer output for the meter lights is losing connection across the board. I'm thinking cracked trace. I have it bypassed for now so I could get the rest of the unit going. Bias both channels dialed in easily and steady. Adjusted the meters no problem. I didn't set the current limiters but I recently bought a scope (Tektronics) off eBay and this weekend I'm gonna try and figure out how it works. DC offset is high...82.6mv right.....82.4mv left. The original 798s are the only transistors I did not replace. I thought I would give them a try but no, not gonna work. I'm gonna see if I can get some matching pairs and replace them. The faceplate and handles are at the anodizing shop and should be ready end of next week. I have an original Pioneer power cord on the way. The wooden bumpers I used are SX1250 end trims that I had in my parts pile. They'll have to do until I can find the correct bumpers but I'm not holding my breath for that, parts for these are slim pickins. The original gain pots were trashed. I ordered Alps stepped pots from Mouser and some new reproduction SX1250 volume knobs complete with set screws and allen wrenches to use on them. A little overkill but they look and feel very nice. Oh yea, IT ROCKS!!! IMG_20191206_203553262.jpg IMG_20191206_203538426.jpg
 
I have found that 2SA798s age very poorly. You can do the dual KSA992 thing or there are some NOS 2SA798s on eBay that appear to be real.
 
EastPoint said:
I have found that 2SA798s age very poorly. You can do the dual KSA992 thing or there are some NOS 2SA798s on eBay that appear to be real.
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I have a pair of those 798s from eBay but I haven't heard from anyone that has actually tried them. I know the matched 992s work good in my other Spec 2.
 
rhodus said:
Got it. Loose fuse connection @ FU-2 on the power supply board. Also, one side of the xformer output for the meter lights is losing connection across the board. I'm thinking cracked trace. I have it bypassed for now so I could get the rest of the unit going. Bias both channels dialed in easily and steady. Adjusted the meters no problem. I didn't set the current limiters but I recently bought a scope (Tektronics) off eBay and this weekend I'm gonna try and figure out how it works. DC offset is high...82.6mv right.....82.4mv left. The original 798s are the only transistors I did not replace. I thought I would give them a try but no, not gonna work. I'm gonna see if I can get some matching pairs and replace them. The faceplate and handles are at the anodizing shop and should be ready end of next week. I have an original Pioneer power cord on the way. The wooden bumpers I used are SX1250 end trims that I had in my parts pile. They'll have to do until I can find the correct bumpers but I'm not holding my breath for that, parts for these are slim pickins. The original gain pots were trashed. I ordered Alps stepped pots from Mouser and some new reproduction SX1250 volume knobs complete with set screws and allen wrenches to use on them. A little overkill but they look and feel very nice. Oh yea, IT ROCKS!!! View attachment 1692652 View attachment 1692653
Click to expand...

Just in case I (or somebody else) end up needing to replace the pots as well, would you have the reference of the ones you got? Do they for easily?

Thanks!
 
I simply cannot imagine tackling that poor thing.

I live for these threads, tho I have zero tech skills. Super cool to save this legendary amp.
 
rhodus said:
I have a pair of those 798s from eBay but I haven't heard from anyone that has actually tried them. I know the matched 992s work good in my other Spec 2.
Click to expand...

I picked up a bunch and they seem to work fine. I can never get the 992 matching thing to work for me, for whatever reason. It's just way too much trouble.
 
Well, I've been checking out this scope and here is what I have...the left channel starts clipping at just above 41 volts (210 watts). The right channel sounds terrible at just above 31.5 volts (124 watts) and shows this waveform....

Can anyone tell me what this means?
IMG_20191208_171226598.jpg
 
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