Gyraf Pultec with XS1100 very low signal

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crisotop

Well-known member
Joined
Feb 22, 2007
Messages
720
Location
Linz / Austria
hey all,

I've just finished both my Gyraf Pultecs, but having some trouble. I'm sednig in a balanced +4dBu Signal from my converter, but the I'm getting nearly no signal back. It sounds weak and thin, and even a bit distorting. I'm using both xs1100 as in and output trafo, with the 2k2 termination resistor (as indicated for use with ll5402) in place. tha passive section seems fine, at least i can hear the controls working.

Any suggestions?
Thanks!
Christoph
 
send in a sine/ test tone. check voltages. ac and dc. how much ac drop across flter? gain in make-up amp?
edit:ac pre and post edcor?--could be wired-up wrong.
 
heater is fine, anode is about 300, pretty high, but shouldn't degrade sound, right?

edcor is hooked up via adapter board from purusha, but will double check the wiring....

thanks! christoph
 
..remember to short output/input minus-phase to ground (XLR pins 1+3) when running unbalanced.

+300V HT is on the high side - you'd probably have the tube for longer time, if you lower the working voltage to some +250V (measured when heated up).

To do this, the resistor between the two ht-capacitors will have to be larger - try e.g. 22 KOkm..

Jakob E.
 
Check the ratios of the In and out transformers. If it's not too much work, try to eliminate the transformers. This way you can isolate the circuit and the transformers. When possible I test the circuit without the I/O transformers. Is it possible that the ratios are exactly backwards?

If it sounds distorted, it sounds like a problem with the output stage. I would just run an unballanced signal into the output stage, and monitor the output without the Edcors. That would be my first test. Then insert the filter. Then the output transformer, then the input transformer.

Vetsen
 
EDIT: Oh gosh, I put in ECC83 instead of 88s - I really should have checked that first.....


Input stage is fine, signal is passing through the passive filter network and it seems like the gain makeup stage is not doing it's job, the signal is about the same from filter out to the output cap. both transformers are passing signal.

thanks for all your help.
christoph
 
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