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  #1  
Old 07-25-2011, 10:28 PM
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Proprietor Springvale Studios
 
Join Date: May 2008
Location: Ipswich UK
Talking Help Transistor amp Chaps!

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I was looking at this blown old traynor 25 guitar amp that someone abandoned at the rehearsal room and was shocked at the obvious quality and adaptability of the two printed circuits.
They are covered in very nice mullard 280 tropical fish caps,
mostly discreet transistors and hardly a lytic cap in there.
So as is my wont I threw the box speaker and chassis in the
bin as the TIP 100 and 105 Darlington Transistors are fried
i just binned them too, they are not getting replaced either. (now its got some serious power supply +- 31 volts & +-18V) Built it into a rack case with the pre amp board in a nice shielded partition, hooked up the line out and was very pleased with what i heard, tried all the equivalent op amps in the solitary op amp socket. Interesting!
Now the thing is, assuming the thing is useless as anything other than an interesting pre amp with loads of crunch gain a mid boost switch and LF cut and a HF boost. Oh and a cool acutronics reverb. Zing!
Is there any of the main amp board that could be used to drive an output transformer for balanced line out.
and if so across which components in the PSU main amp board would you fit it and about what sort of impedance would I need for the primary:

Its just that I inherited a pile of very high quality western electric +24 dB 20 Hz to 20k audio transformers of all different and some very low impedances and types.
I even have one with a measured 4.6 ohm dc resistance on 1 & 2 and 31.1 ohms across 3 & 4.
marked MO 47161-50 73/47 if that means anything to anyone.
I have some that measure 15 ohms dc each side of a center tap.
Now where shall I stick one across chaps, before the diodes?.
Or the whole hog, - the Tip 100/105 pair of course.
I may just use it as a buffered out, to drive a bridge rectifier for an analogue VU meter
  #2  
Old 07-26-2011, 11:27 AM
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Join Date: Aug 2004
Poke around here.

Balanced Transmitter and Receiver II

Just connect to where the pre-amp connects to the power amp.

If you really want to use the transformer, you can add one to the output of such a circuit. I don't see any need to though.
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  #3  
Old 07-26-2011, 08:51 PM
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Join Date: Nov 2003
Location: St Louis
Those circuits are not safe with phantom power, maybe another part of the site shaows one that is.

Transformers make it perfectly safe with PP. use a DC blocking capacitor between driver and transformer, along with maybe a "build-out" resistor because the transformer may need it..

Also, a good place to get the input is top of the master volume, since that avoids send level changes when master is adjusted.
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  #4  
Old 07-27-2011, 06:29 AM
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Proprietor Springvale Studios
 
Join Date: May 2008
Location: Ipswich UK
Talking Argh!

Quote:
Originally Posted by Jerrold Tiers View Post
Those circuits are not safe with phantom power, maybe another part of the site shaows one that is.

Transformers make it perfectly safe with PP. use a DC blocking capacitor between driver and transformer, along with maybe a "build-out" resistor because the transformer may need it..

Also, a good place to get the input is top of the master volume, since that avoids send level changes when master is adjusted.
Cheers for your help chaps!. I am fooling about with the build out resistor choice at the mo, cant make up my mind as to weather driving the transformer into saturation is always what I want, so I have drilled yet another micro switch hole for the front panel. There is a couple of the transformers I have found that sound very good, so the temptation is to get yet another DPST and have two transformers. But then there is this other transformer in the box thats not too crap, feed from the long tailed pair in the main board, Now thats two more male XLR sockets than planned, perhaps I should have started with 3U, oh god! I have bad component gas. Somebody stop me!.

PS. The big old western meter I have has a failed, what appears to be, a cuporus oxide diode in the driver bridge?, I cant find any info about them at all!
Does anybody know what's the lowest forward resistance diodes you can get today that will drive the 500 uA meter well.
  #5  
Old 07-27-2011, 08:40 PM
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Join Date: Nov 2003
Location: St Louis
The meter and the copper oxide rectifiers go together.....and make the meter read right. It's a "system".

If you get some "schottky" diodes, the lowest current you can find, and choose a series resistor correctly, you might get close.

But copper oxide have a very low threshold, and have a variable resistance characteristic..... they are perfect for level meters.
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