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Author Topic: SUBSTITES FOR 30L-1 METER AND POWER TRANSFORMER AND POWER SWITCH?  (Read 4696 times)
N6QWP
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« Reply #30 on: September 05, 2018, 03:10:07 PM »

Thanx Carl....sounds like what I am trying to accomplish with this old wreck.  Wondering what voltages and available current you are using for 811A's.....and for 572B'S?

Are you using the original supply?  Or, have you adapted something else?  

Are you bringing up the HV gradually, or just letting it go full bore....(after letting the filaments cook for how long?)

I just purchased four more old RCA 811A's and three Cetron 572B's...and still have four old 811's.  All need testing.  Don't want to blow them up unnecessarily.

« Last Edit: September 05, 2018, 03:24:13 PM by N6QWP » Logged
G3RZP
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« Reply #31 on: September 05, 2018, 11:06:44 PM »

If your 1N4508s came from the same batch, I wouldn't even bother with the capacitors. I would suggest another RF Choke between the end of the one Collins used and the PSU and then a 0.01mFd 3lV disc ceramic to ground to keep RF away from the electrolytic chain.

Electrolytic caps don't like RF current through them...
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KM1H
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« Reply #32 on: September 06, 2018, 07:49:17 AM »

That amp originally had 4 811A's and later they switched to 572B's. I configured the PS for a FW doubler or a bridge using a HV switch. A Variac controls the voltage and a separate filament transformer is used. I also use it to regetter those tubes since I deal with so many amps using them.

Carl
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KM1H
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« Reply #33 on: September 06, 2018, 04:01:26 PM »

BTW, an old original Dahl catalog lists 16A. Sounds like a typo and I hope Hammond is not building them to 11A otherwise a lot of smoke.

The Ameritron xfmr is used with both amps and is one of the best bargains on the planet. Ive used several in projects plus replace in other old amps.

Carl
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N6QWP
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« Reply #34 on: September 06, 2018, 04:58:36 PM »

So in the 160-10L, I deduce that you are using their original transformer with another filament transformer?  Still trying to determine how much voltage you have available to test and getter the 811A's and then the 572B's?

From what I have been reading, the 572B's will require more than the 811A's can handle to properly test them.  Thus my inquiry about whether the transformer is original....or a substitution?  

I understand that the variac will reduce the HV for 811A's-if the voltage available is too high for them.  I read that the original Dentron transformer provided about 2KV (about the same as my original 30L-1 with the Young board)?

Thanx Carl.....would want to verify the Peter Dahl info before going any further with it.  Can contact Ameritron for their info.


« Last Edit: September 06, 2018, 05:15:48 PM by N6QWP » Logged
KM1H
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« Reply #35 on: September 06, 2018, 05:45:04 PM »

Read post 32 again
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N6QWP
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« Reply #36 on: September 06, 2018, 06:26:35 PM »

OK....was just hoping that you would share with us, what the actual highest voltage is that you are able to develop with your changes?  When chosing a substitute transformer, that will help in my selection.  Thanx
« Last Edit: September 06, 2018, 06:30:56 PM by N6QWP » Logged
KM1H
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« Reply #37 on: September 07, 2018, 10:21:16 AM »

All I did is reconfigure the rectifier circuit so both the 811A and 572B voltages were produced, about 1000 and 2000V at no load but 1500/3000 also works or anything in between. The Variac sets whatever I want down to zero.
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N6QWP
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« Reply #38 on: September 07, 2018, 10:41:08 AM »

Thanx Carl--That's what I needed to know.  Now "the Hunt" begins in earnest.  

I read somewhere on these threads, I thought, that the 572B's needed more than 2K to getter and also to stress them a bit?  Something about when substituting the 572B's in a 30L-1, they weren't getting enough voltage (perhaps it was current?).

That was probably more about whether they will actually last longer in a 30L-1.  I guess all we are doing with a test platform is checking for gas and trying to weed out the ones that are obviously bad to eliminate flashovers.

If you have been able to do it successfully at 2K, that's what I was wondering.  As always, your advice is greatly appreciated.
« Last Edit: September 07, 2018, 10:46:24 AM by N6QWP » Logged
N6QWP
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« Reply #39 on: September 12, 2018, 07:39:27 AM »

****  30L-1 TRANSFORMER PRIMARY WIRES SEEM VERY LIGHT DUTY???  ****

Just had a chance for a closeup inspection of a removed Collins 30L-1 ORIGINAL power transformer.  I was amazed that the AC PRIMARY WIRES appeared almost TINY for handling the amount of current that it does.

Whle they are solid, the diameter is much less than a standard computer power cord.  Anyone familiar with this amp care to make any observations....or explainations?

I seem to remember old TV transformers that had heavier wires (which were stranded)....and they handled lighter loads.

When I search for substitute power transformers, should this be a concern....or are light wires not something to worry about?  Or, is the fact that they are solid and not stranded the reason that the can be so much lighter?

For a transformer that is that size and weight, I expected much heavier wires.

The AC line fuses are 7.5 amp.  It is wired for 117 vac.  What am I missing here?
« Last Edit: September 12, 2018, 08:00:15 AM by N6QWP » Logged
G3RZP
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« Reply #40 on: September 12, 2018, 09:12:18 AM »

It has two individual 117 volt primaries. Each is switched by one pole of the double pole power switch and each is fused originally at 8 Amps. So the leads don't need to be as thick, and the fuses are the same value for 117 as for 234 volts.
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N6QWP
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« Reply #41 on: September 12, 2018, 09:23:15 AM »

G3RZP--Thanx, I was just typing as you replied.  I just noticed that about the dual primaries while reading about the supply online.  That would explain the diameter of the wires, since the load is split between the two....and they could be half the size of a single primary transformer.

That will answer the question about searching for a replacement transformer with a single primary.  One will require thicker primary leads, as I was pondering.

I will also be searching for a heavy duty filament transformer, so that I can control the HV for testing separately with my variac.

« Last Edit: September 12, 2018, 09:26:13 AM by N6QWP » Logged
KM1H
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« Reply #42 on: September 12, 2018, 09:35:36 AM »

Quote
I read somewhere on these threads, I thought, that the 572B's needed more than 2K to getter and also to stress them a bit?  Something about when substituting the 572B's in a 30L-1, they weren't getting enough voltage (perhaps it was current?).

It is all about current for gettering which is what gets the 572B anodes glowing a bit red.
First of all I dont want any tube arcing over as that all to often destroys it.

Voltages up to about 1200V will not sustain an arc in even a moderately gassy tube so the LV switch position is where I start testing and looking for telltale glows.

In order to regetter a 572B at 2000V or less I use an old 70's HP 0-20V PS for bias (Any variable DC supply will work and one with adjustable current limiting is best) and crank it up until I get a nice red color and let it cook for an hour or more.....I forgot...use a small fan on the glass.

Carl
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N6QWP
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« Reply #43 on: September 12, 2018, 02:23:16 PM »

Thanx again Carl.  Could you, perhaps, for clarification, describe exactly what YOU look for inside the tubes to indicate gas?  Color that might be ok?  Color that definitely indicates impending doom?.....AND WHERE?  (For BOTH 811A and 572B Tubes)

There seems to be some difference of opinion and it would be great if you could clear things up....once and for all.
« Last Edit: September 12, 2018, 02:34:24 PM by N6QWP » Logged
KM1H
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« Reply #44 on: September 12, 2018, 04:06:42 PM »

Blue on the glass surface is OK and common with power tubes.

Blue down in the filament to grid area is outgassing. Also often seen in RX tubes that have been run very hot due to leaky paper bypass caps in the AGC line to the grid killing the bias voltage. Those tubes should be tossed.

Purple anywhere is AIR and precedes the white getter. If not too bad it could be absorbed into the anode depending upon the actual gas. At best it is temporary.

Carl
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