How to bring up new old amp with Variac and DBT

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#25
All the TO3,s are MJ15024

The epoxy filled tops were supposed to stop high frequency ringing but every other amp after this series didn’t include this mod.

The input cap should be a Sideral 4.0 mf as that was what he used towards the end of this series

The DCO is typical but know this amp is at least 35 years old and the PS caps should be changed out as usual
Matching input transistors will bring down DCO noticeably

I have a dual mono unit ( 2 trans ) that was modded at his shop when he was in
Paramount ,CA but one side needs work and haven’t used it in years

Bedinis drive electrostatics very well BTW

Regards
David
 
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#26
egellings said:
My problem with the DBT is that I cannot find any incandescent lamps in the stores. .
Click to expand...

"Halogen" is same-as for this purpose.

The Eubank Albuquerque Home Depot has nineteen 4-four-packs of 100W equiv (72W actual) in aisle 5 bay 5.
 

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#27
It is the preamp. I fired up the system this morning and got the normal hum and wondered if I would get the same with other inputs. This is without anything plugged into those inputs. Every input has it's own strange noise and volume level and when I flipped the Tape In toggle switch all the inputs went down by 20db or so. This is not a hotshot, cool cat-daddy, top of the line preamp so it goes on the shelve.
 
#28
I just ordered a Variac and have two Hybrid Tube amps that had some problems
My question is this. Before I start with the power up when using the Variac, should I have a cheap speaker hooked up to the outputs? Or what kind of summing load ? Or if any ?
 
#29
Use a 10 ohm power resistor for each channel for testing with all tube amplifiers.
Using a speaker is only for after the amplifier has passed all initial testing.
I use junk speakers only after testing while burning in, to listen for noises, etc.
 
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#30
rayma said:
Use a 10 ohm power resistor for each channel for testing with all tube amplifiers.
Using a speaker is only for after the amplifier has passed all initial testing.
I use junk speakers only after testing while burning in, to listen for noises, etc.
Click to expand...


Thanks
Just for my understanding, how did you come up with 10ohm power resistor ?
Remember this is a hybrid power amp
Tubes for the input and solid state for the power output . If that makes any difference
IMG_5353.jpg
IMG_5351.jpgIMG_5335.jpg
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#32
Sometimes a solid state amp will be ok without a load, sometimes not.
I don't recommend those resistors, which are a regular resistor in a metal case.
They must be bolted to a large heat sink to dissipate much power.
Without a heat sink they might be good for 5W-10W each.

Some of these in series-parallel to increase their power rating would be fine.
Dayton Audio DNR-10 10 Ohm 10W Precision Audio Grade Resistor
 
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#33
I made up what Rayma comments on but genuine steel cased Dale (Vishay and others ) with the full manufacturing coding /value etc .
I took them from a major electronic communications companies scrap PCB,s the 10W resistors are only half the size of the ones shown but did not overheat on a 50W heat-sink.


I am very dubious about the ones shown as no genuine information is imprinted on them only the value and even then the print on mine is fine not looking as if its stamped on .
 
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