813 amp and old choke

[kheper]

I am gathering parts for a new 813 SE amp, along the lines of Pete Millett's design. A question is: I have a big, Stancor choke (8Hy @ 300ma). The insulation is rated for 3000V, but no max working voltage is given in any Stancor manual. Is hitting this old choke with ~800Vdc a wise move?

[Frank Berry]

You can always put the choke on the negative side of the power supply.
This was often done in transmitters to keep the choke at near ground potential.

[M Gregg]

Originally Posted by kheper

I am gathering parts for a new 813 SE amp, along the lines of Pete Millett's design. A question is: I have a big, Stancor choke (8Hy @ 300ma). The insulation is rated for 3000V, but no max working voltage is given in any Stancor manual. Is hitting this old choke with ~800Vdc a wise move?

Megger test it. If it clears 500V try 1000V.. If it clears that soak test it...apply your dc voltage with no load in a bread board lash up! for 3hrs or so..Make sure its fused..

If this clears then try loading it... Just make sure you don't touch the laminations or metal work when its on! There is no telling how long it will hold up..then again I have used old chokes and had no problems. As long as its on an earthed chassis..

As above if its on the earth side of supply it is less lightly to flash over!

Regards
M. Gregg

[hemgjord]

If it is rated for 3kV DC it should be OK to use it up to 3kV(peak). If it is hi-pot TESTED for 3kV you should allow for a decent safety factor. I would guess that 800V DC is perfectly OK.
If you are still worried connect the choke on the ground side.

/Olof

[kheper]

Here is the 1948 manual. (part number = C-2308)

http://www.bunkerofdoom.com/xfm/STAN...48_WEB/010.jpg

The voltage at which the integrity of the insulation breaks down is 3KV R.M.S.

Did they do "Hi-Pot" tests in the 1940s? Thanks guys. I'll bread-board as was suggested. The choke will not be pushed to anywhere near 300ma with this amp.

[M Gregg]

Originally Posted by kheper

Here is the 1948 manual. (part number = C-2308)

http://www.bunkerofdoom.com/xfm/STAN...48_WEB/010.jpg

The voltage at which the integrity of the insulation breaks down is 3KV R.M.S.

Did they do "Hi-Pot" tests in the 1940s? Thanks guys. I'll bread-board as was suggested. The choke will not be pushed to anywhere near 300ma with this amp.

In 1940 most if not all electronics were High Voltage....so yes they did test.
Some of the car radios were low voltage tubes..most needed a reed vibrator for the HT from the car battery..

If you ever get chance to see the inside of troop carried radios they are a work of art...compact isn't the word (OK they are big) however they look like a big valve hand made chip..LMAO. (Some people have a hobby rebuilding war equipment)...Not me, I used to know a few..in a previous life/job.

Regards
M. Gregg

[kheper]

I meant "Hi-Pot" as in the modern battery of tests performed on electrical devices, not just the insulation test.

http://www.bunkerofdoom.com/xfm/stan...stan66_019.jpg

"Insulation Test Voltage: Twice allowable RMS Working Voltage plus 1000 Volts"

They do not give the "allowable RMS Working Voltage" in the manuals I can find. Some are incomplete, however. Extrapolating from the above quote, 800V should be ok, but the choke is ancient.

[M Gregg]

Originally Posted by kheper

I meant "Hi-Pot" as in the modern battery of tests performed on electrical devices, not just the insulation test.

http://www.bunkerofdoom.com/xfm/stan...stan66_019.jpg

"Insulation Test Voltage: Twice allowable RMS Working Voltage plus 1000 Volts"

They do not give the "allowable RMS Working Voltage" in the manuals I can find. Some are incomplete, however. Extrapolating from the above quote, 800V should be ok, but the choke is ancient.

The biggest problem with old windings was mould growth and insulation breakdown..It does not matter what tests you do, insulation test and soak test standing idle is the only way to go..no they did not do modern type Hipot tests then again stanging on the bench for a week running full throttle helped..All previous data is void until proven to be OK..if it was me I would ignore the data sheet except for" it could once perform at this level" now its only as good as the tests i can prove..of course you could test to destruction and know for sure..lol Then again the next one would be unknown as well!

I ran a single ended O/P Tx from off a dump standing in the rain with rotting wet wood around it (the case) in a fun guitar amp still going after 6 years!
I would not be tempted to dip it in insulation varnish I know it can dissolve some of the old shellac and stuff it!

Regards
M. Gregg