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Author Topic: Help Debugging Bluesmaster 50  (Read 996 times)
mwdavis14
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« on: February 13, 2014, 07:21:31 PM »

I'm on my second time through trying to fix this amp and am at a loss.  I'll give you the history briefly, and then where I stand presently.

I finished build, which was done slowly and by the book.  Went through power up w/bulb limiter w/o issues.  Hooked up guitar and speaker, and there was a horrible scratching w/the vol pot and only clean tone with limited volume.  Came to discover that the vol pot was bad, and I had used too much solder when hooking up V1 and V3, and had blocked some of the pins so those two tubes were not working.  Purchased new vol put (CTS) and new tube sockets.  Pulled those items and hooked everything back up.  Double checked continuity across everything w/DMM.  All checked out.  Power up w/bulb limiter again w/o issues.  All tubes heating properly, no sockets blocked this time.  Hook up the guitar and........ Nothing.  No sound.  Not a peep.

Anyone have an idea of where I go from here to debug this thing? 
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mwdavis14
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« Reply #1 on: February 15, 2014, 09:46:38 AM »

Some additional information:

Here are the pin voltages (measured w/the tubes out - 50w amp):

V1 1: 211 mv
2: 0
3: 0
4: 3.58 v
5: 3.58 v
6: 200 mv
7: 0
8: 0
9: 3.58 v

V2 1: 222 mv
2: 0
3: 0
4: 3.58 v
5: 3.58 v
6: 211 mv
7: 0
8: 0
9: 3.58 v

V3 1: 241 mv
2: 0
3: 0
4: 3.58 v
5: 3.58 v
6: 229 mv
7: 0
8: 0
9: 3.58 v

V4 1: 0
2: 3.59 v
3: 218 mv
4: 219 mv
5: -46 v
6: 222 mv
7: 3.59 v
8: 0

V5 1: 0
2: 3.59 v
3: 218 mv
4: 219 mv
5: -46 v
6: 222 mv
7: 3.59 v
8: 0

With the exception of the heaters, all readings are in DC. "mv" is not an error, that is what the DMM is measuring.

Bias readings from original post were taken from the bias measurement points, which have a resistor. The pin #5 voltage reading referenced above is taken directly from the pin socket. I currently have no idea how to measure bias at the board, but will read up on it and try to post that.

Pictures to follow as well. Hopefully someone can help me here.

Could this be a transformer or choke issue? As I stated in original post, this build was done slowly and very meticulously. Continuity exists across all points. I have traced all wiring to the board positions to double check continuity, and all of that checks out. Layout strictly followed Ceriatone's posting. There are a couple of mods, but these were standard Ceriatone mods and followed Nik's layouts to the letter as well.
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