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In Reply to: RE: Mikey Helps The Technically Challenged - Me. posted by geezerrocket on October 14, 2014 at 11:03:37
OK, now that it is fixed - what went South?
Inquiring minds want to know.....
Follow Ups:
6bq5;
It had a obviously fried resistor(s) of the wrong value when I received it.
Per Mikes' instruction I changed out the two wired in series fried resistors (to valve 9) to a single 1.2k 10 watt wire wound. I then turned it on and watched all the pretty smoke - Bwah Ha Ha!
Mike was kind enough to call me on his lunch hour and had me pull the output tubes, turn the volume down, then power it up and begin inserting 7591 tubes one at a time until the smoke appeared - Bad tube. A technically astute person would have noticed the cherry red tubes, but no one has ever accused me of being such. The bad tube was a JJ 7591S. I have had nothing but trouble with JJ power tubes, however, I have had good results with JJ small signal tubes. Anyway, I had no idea that could/should be done.
I am in the process of getting rid of the toggle on/off switch that was installed when the volume detent failed.
I will be getting a hold of Jim McShane for some grid resistors, Russian K40 pio .1uf coupling caps, matched quad of 7591's, and a couple of 12ax7 lps tubes. After that, it's off to the garage to power a pair of Heresy's.
Again; Thanks to Mikey and the other tech savvy members here that help the knuckle daggers like me on this forum.
This is precisely why I will be sending Mike my HK Citation II and AR SP3 (acquired very recently) later this winter. He sounds pretty excited about doing surgery on the SP3.
At this time he has my Sherwood S-5000 just about ready for shipping - Should be fun!
I was a vegetarian for 15 minutes, until the main course.......Meat; It's the right thing to do. Romans 14:2
Thanks-
I asked in part as I once had a Scott 299 - that blew-up one night - I left it on....
a big wire wound resistor broke and took out something else -
never went to fix as I was told that the Power Transformer was shot -
I miss that unit - but
I have better toys today....
While it is work , recovery from a failed power transformer in Scott 299Cs, 299Ds, LK72As, and LK72Bs need not be hideously expensive. The "beefed up" replacement power trafo Triode Electronics sells for Dyna ST70s can be adapted to the need.
Use 1 of the 2X 6.3 VAC windings to energize the 6 power section tubes. Voltage double, with Schottky diodes, the other 6.3 VAC winding and 7812 regulate the resulting DC, providing for the 4X 12AX7 heaters. Half wave rectify the bias tap (a Schottky diode is preferred) and CRC filter the resulting "raw" DC to obtain the C- supply.
The scheme outlined above is made possible by the fact that the heater current draw of a 7591 is less than that of an EL34. :> D
Eli D.
As always, you are a fountain of information, Eli. Is there anything that works with a Scott 222D?
Dave
Contact Heyboer. You may have to send the failed item in. Unfortunately, I am unaware of a suitable off the shelf power transformer.
Eli D.
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