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I need help figuring out this part of my OTL

174.50.82.179
Posted on April 15, 2020 at 09:50:33
djn
Audiophile

Posts: 1955
Location: Albuquerque New Mexico
Joined: January 15, 2003



Hi guys. I didn't want to start a new thread but my dummy load resistors will be here in the morning and I don't fully understand this section of my amp.

As you can see by the picture in the front of the amp are 2 DPDT toggles and a 5 position switch. On top of the amp are 4 dial-in thingies and a meter.

This all seems to correspond with the schematic also attached.

Buy... I have no idea what to do with it and I can't find anything on the net.

 

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RE: I need help figuring out this part of my OTL, posted on April 15, 2020 at 09:51:25
djn
Audiophile

Posts: 1955
Location: Albuquerque New Mexico
Joined: January 15, 2003



Here is the schematic

 

RE: I need help figuring out this part of my OTL, posted on April 15, 2020 at 11:15:21
6bq5
Audiophile

Posts: 4393
Location: SF Bay
Joined: August 16, 2001
 Couple of points-
1: the schematic shown looks like the PS only
2: the 5 position switch and meeter looks like it is set up to measure the parameters of the Output tubes, and the black thin knobs are probably connected to Potentiometers to adjust the voltages based on the switch setting and meeter reading -

I would need to know a bit more to provide further help - but OTLs are not my forte-
Happy Listening

 

RE: I need help figuring out this part of my OTL, posted on April 15, 2020 at 15:17:42
Cory M.
Audiophile

Posts: 1172
Location: Midwest
Joined: April 10, 2005
 Agreed with 6BQ5- is there a an audio portion of the schematic?

It appears that each potentiometer would control a bank of 3 output tubes, a positive rail trio and a negative rail trio for each channel to adjust & balance offset. So, the two trios per channel should be matched reasonably well within their +/- group. The 5 position switch may be center off, R ch. + and -, L ch. + and -. Now, how the output tubes are grouped on the chassis, and which pot. controls which group is another question...

Anyway, that's just a guess though- might need to do some tracing if there's no tube schematic available.


Cory


 

Schematics link to this amp, posted on April 15, 2020 at 15:27:55
djn
Audiophile

Posts: 1955
Location: Albuquerque New Mexico
Joined: January 15, 2003
 Here is a link to all 4 of the schematics for this amp. Thanks for the help guys.

https://www.bonavolta.ch/hobby/en/audio/6as7_2.htm

 

RE: Schematics link to this amp, posted on April 15, 2020 at 16:25:53
Cory M.
Audiophile

Posts: 1172
Location: Midwest
Joined: April 10, 2005
 Now we're cookin'.

So, it appears that the +/- rails are separated by tube sections instead of bottles. Meaning, a positive and a negative section exist in each 6AS7 dual-triode tube. So, any matching attempts would be more difficult to sort, and probably moot.

Those resistors that you want to insulate /secure are on the grids, pins 1&4, so no HV, but you still don't want them shorting to anything. ;)

**Edit- I see that the resistors in question are infact on pins 3&6 (cathodes), as stated earlier. I was looking at the schematic, not the picture. Sorry.**

Do you know the bias point to set the 6AS7's at?

Still need to determine the layout of the output tube positions on the chassis- that will need to be traced out... Or not- you could just install the tubes and go with it. Are the B+ and bias supplies fused?



Cory


 

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