hv transformers

[W2VW]

Late BC-610 oil filled and T-368 iron can withstand full wave bridge operation with a choke input even though they have a center tap. The center tap is insulated.

[K5UJ]

Frank Slab,

this vy timely for me; i have old thordarson iron with CT, 200 lbs 1A 3250 - 0 - 3250 & 872A s.s. replacements

rob

SCHWEEEEEEEEEEEET! ! ! ! ! ! ! ! !

That sounds like a really nice chunk of iron! ! ! ! ! !

Thanks Frank, yeah it looks like it gg to be a good one.  There is also a filter cap that's huge.  12 inches tall, 18 inches deep and 3 or 4 wide.  looks like a small gray briefcase except for the two porcelain insulated contacts on top.  The porcelain is at least an inch tall.

Yeah Dave I would have done the same thing maybe had I not read the warnings here.  That stinks what happened to ur iron.  The stuff is heavy enough when it works but heaving that weight when it is dead is the pits.   I sure have learned a lot from you guys.

Rob

[The Slab Bacon]

Rob,
      If that is an old, open framed transformer, and hasn't been used for a loooonnnnggg time, I would seriously consider baking it out and dunking it in a bucket of varnish before using it for any length of time. It is cheap insurance that it will continue to work without an insulation brakedown failure. At 6500vac old insulation will be a lot more likely to show its age.

If it is a modern open frame transformer I wouldn't worry too much about it, as the insulaing material will be something much better than "fishpaper". If you run a cap input filter (C-L-C) you will probably still get 3500vdc (or better) under a load. You just need to cobble up a step-start to make it easier on things when firing it off.

[The Slab Bacon]

I HAD a pair of those 25 years ago. I loaned them to a friend and told him just to use them at 3KV until he could find something better. He reconfigured them to FWB and turned them to scrap.

Dave,
        Whak kind of voltage was he looking for? ? ? ?     

[KM1H]

Rob, look in an old HB, either brand, and read up on "critical inductance" in the filter. With too low an L in C-L-C and too big a cap the transformer voltage and current can soar to destruction even with no load. You also need a decent bleeder whenever the HV is on.

You can only suck so much POWER out of the transformer and C-L-C or L-C it doesnt change. Since you cant use a fat input cap with vintage iron the peak voltage is the only difference and the L-C offers superior regulation and less distortion on SSB and AM modulators.

Carl
KM1H

[W2VW]

I HAD a pair of those 25 years ago. I loaned them to a friend and told him just to use them at 3KV until he could find something better. He reconfigured them to FWB and turned them to scrap.

Dave,
        Whak kind of voltage was he looking for? ? ? ?     

6KV

A quad of T-368 xfmrs with secondaries parallel and primaries across either side of the mains later filled the bill.

[K5UJ]

Okay Frank, it looks like one of the CHT style ones--it has the ends closed; not open; I was gg to run it through a 20 to 30 A variac at least at first;

Tnx  Carl; I should have mentioned this earlier--I'm starting out building a single 4-1000A linear amp; later perhaps adding a second 4-1000 & using a Ranger as an exciter; or modulating the single 4-1000A but for now, I'm just gg to try getting a single 4x1 on the air in g.g. triode service and learn about the supply, TR switching, matching the cathode 110 ohm, the tank circuit and all the rest.  But, having said that, I have the old handbooks and am adding to the collection; just purchased a 1943 Terman handbook--i was doing the power calculation last night; am glad to have been through some of this with pair 3-500 re Ep, IMD, plate dissipation, Ip, supply power and current for reasonable parameters for clean AM linear operating (not to mention the need for augmented cooling) so I have been reading the 4x1 data sheet and getting a feel for how to handle it.  However the data sheet I have seen do not cover g.g. triode use not surprisingly, so I'm glad to mine the archives here and you guys who have been down that road    looks like a single 4x1 can be run at 3.5 KV for around 300 w. and easily dissipate the input loss but that was just a first number crunch.

Rob

[K5UJ]

Here's some photos....

[KM1H]

That looks like the one I fried about 26 years ago trying to run FWB on a 3CX1000A7 2M amp. It lasted about 2 weeks of very intermittent use 1500W SSB. Im still using a pair of 12uF @ 5kV oil filters as in your photo on that amp.

Not sure if its the replacement xfmr or the caps but that PS has better regulation than anything else here. 3900 to 3700V no load (except for 150K of bleeder) to full load of 900 ma.

Carl
KM1H

[K5UJ]

That looks like the one I fried about 26 years ago trying to run FWB on a 3CX1000A7 2M amp. It lasted about 2 weeks of very intermittent use 1500W SSB. Im still using a pair of 12uF @ 5kV oil filters as in your photo on that amp.

Not sure if its the replacement xfmr or the caps but that PS has better regulation than anything else here. 3900 to 3700V no load (except for 150K of bleeder) to full load of 900 ma.

Carl
KM1H

I was wondering the specs on the capacitor.  A friend guessed 5 KV and ventured 50 uF.  nothing is on the cap to give any information and the schematic for the partially built 4x1 amp has nothing on it for the h.v. supply.  it is a schematic for the standard single 4-1000 g.g. linear amp.   So, I'm glad to know what kind of cap I have.  So, 12 uF.  I have to look at the bank of bleeder resistors.  don't know what is there off hand, but from what I know, 12 uF isn't enough; I need about three times that, or around 30 uF I believe.

Rob

[KE6DF]

A capacitor meter or a DVM with a capactance scale should give you the answer.

But, no way to tell the voltage that I know of.

The voltage might be higher than 5KV given the big insulators.

[K5UJ]

yeah, stupid me I should have thought of that.  duh.  i have a fluke 115; it will tell me.

[W2VW]

Don't forget to leave a set of handcuffs across that bad boy when you work on it.

They DO recover chemically after discharges and can zap a person to next Tuesday.

[W2PFY]

I have 4  3300 vac hv transformers.Can i put 2 of them in series to double the voltage and 2 in series and parrel to the first 2 to double the current.

They are the same make and part number

Nope

[KM1H]

 

I was wondering the specs on the capacitor.  A friend guessed 5 KV and ventured 50 uF.  nothing is on the cap to give any information and the schematic for the partially built 4x1 amp has nothing on it for the h.v. supply.  it is a schematic for the standard single 4-1000 g.g. linear amp.   So, I'm glad to know what kind of cap I have.  So, 12 uF.  I have to look at the bank of bleeder resistors.  don't know what is there off hand, but from what I know, 12 uF isn't enough; I need about three times that, or around 30 uF I believe.

Rob

I didnt mean to imply that yours is 12uF, I was just going by apparent (eyeball estimated) case size. It could be 4uf @ 10KV as suggested. I have a pair of 25uf @ 2500V in the same case with big beehive insulators like yours. They were utility company phase balancing caps. With 24 uF the ripple is down in the noise on my amp.  BTW, dont lay them down when using.

Carl

[K5UJ]

Well you darn close Carl; you know ur stuff--got all set to put meter on the cap when what looked like faint writing on the side caught my eye.  It was down on the side away from the transformer but with a flashlight and mirror I read 10 MFD 8 KVDC.  Mfr. is Tobe.
 

Lesson here is never ever make assumptions about someone else's homebrew hi hi.  I knew that going in and when in doubt I'm using my parts.  This won't be a problem.  Caps are easy compared to getting iron.  QSL re upright use.

[John K5PRO]

That's Tobe Deutschmann. Look him up on the web, pretty interesting..

[K5UJ]

That's Tobe Deutschmann. Look him up on the web, pretty interesting..

Tnx John, yes vy interesting.   Would have never found it myself.  I googled Tobe and did not come up with much.

Rob

[KM1H]

He is the guy who gave Bill Halligan his start at a real job before he (Bill) left Boston for Chicago and immortality.

Tobe was into anything that he could make money from, a rather colorful character from what Ive read and heard from his family and friends.

Carl