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KD4AL
10-14-2005, 12:52 AM
I'm looking to build a high voltage power supply to use with some tube projects. #But I have discovered that high voltage power transformers are very expensive. #Old junk tube parts-radios are getting scarce. Plus a hate to cannibalize anything that might have a chance of being fixed.

It is easy to find decent sized power transformers with 120vac primaries and low voltage secondaries (6vac, 12vac, 24vac, etc.). In fact, I already own one with a 24vac secondary.

Is there any reason that I could not reverse the connections, apply 120vac to the secondary and get 600vac on the other side? #It all uses the same core. The low voltage winding should usually be of a higher guage wire than the primary, since the low voltage side carries more current. #

I would not try it with a 6vac secondary. #I'd rather not deal with 2400vac if I can help it. Although I might use a 120 to 6vac transformer to heat filaments.

Anyone with experience in this?

Bill KD4AL

W3GER
10-14-2005, 01:05 AM
The insulation on the primary-cum-secondary might not stand up.

73 de W3GERry

K5CEY
10-14-2005, 01:14 AM
Quote[/b] (KD4AL @ Oct. 13 2005,18:52)]Is there any reason that I could not reverse the connections, apply 120vac to the secondary and get 600vac on the other side? #It all uses the same core. The low voltage winding should usually be of a higher guage wire than the primary, since the low voltage side carries more current. #

Bill KD4AL
Bill,

# I'd hate to be in the same room when you try it.

That 24 volt secondary is going to pull a terrific amount of current from the 120 vac wall socket!

May trip the 'breaker and may fry the transformer.

# # # # # John

K5CEY
10-14-2005, 01:25 AM
I just happened to think,
# If you have modest current requirements, you could use several small transformers, say 12.6 filament jobs, and use the 12 volt secondary of one to feed the secondaries of two or more similiar units in parallel, and wire their 120 volt primaries in series. (observing phasing).

Two would give you 240 volts, and so on.

I wouldn't carry it too far because of insulation breakdown, but several hundred volts should be no problem.

# # # # # # # John

K9STH
10-14-2005, 01:26 AM
What you can do is to use two filament transformers wired "back to back" to get up to around 150 to 160 volts which is plenty for many tube type experiments.

You hook one primary up to the 120 VAC then hook two identical filament windings together (and come off of them for the heater / filaments of the project) and then use the 120 VAC primary on the second transformer for rectification. You can also make a voltage doubler, tripler, etc., for some higher voltage (although at a lower current).

For some pretty high voltages (like 1500 to 2500 volts) you can use power transformers from old microwave ovens. However, one side of the secondary is usually connected to the frame so you are limited (at least for safety reasons) to a half-wave rectifier. Some of these transformers require a slight modification to work well in linear power supplies. Do a "google" on something like "microwave power transformer power supplies" and you should get a "fair" number of "hits".

As for putting 120 VAC on any of the lower voltage primaries that is a definite NO NO! You can put 120 VAC on a 240 VAC primary without any problems, but the voltages on the secondary windings are going to be half of what they would be when using 240 volts.

When I was in junior high school (before I was licensed) there was a TV repair shop down the block from my parent's house. The owner kept me in all of the parts, tubes, television chassis, etc., that I could haul off. I did try things like putting 120 VAC on low voltage secondary windings, on things like audio interstage transformers, etc. Blew a few fuses (my parent's house had fuses, not breakers). Then I read a little to see why the fuses blew. Sometimes I wonder why I never caused a fire, got hurt, etc. Guess that I learned fast enough what I could do and what I could not do.

Glen, K9STH

AB6ND
10-14-2005, 03:25 AM
I've used two filament transformers to get an output of 110-0-110 v but had some funny results until I got the phasing correct.
AB6ND

N9XV
10-14-2005, 10:34 AM
Like Glen was saying, the voltage "ratings" must at least equal or be higher than the applied voltage. An old tube type TV makes an excellent source for transformers. For a high-voltage/low-current application the voltage doubler idea that Glen suggested is probably the simplest route to take. But a 600-Volt TV transformer would give your project that nice "boat-anchore" feel.

Kevin

KI4JAY
10-14-2005, 11:23 AM
I work on electronic music gear. Try the company New Sensor. We use HV Transformers in all the tube guitar amps and the prices range from $35-$65. Marshall and Fender are amps that come to mind. Also check with you local music repair shop a lot of times they have them laying around were they scraped an amp out..

Donnie

N8YX
10-14-2005, 12:03 PM
Quote[/b] (KD4AL @ Oct. 13 2005,17:52)]But I have discovered that high voltage power transformers are very expensive. #Old junk tube parts-radios are getting scarce.
Three words of advice:

eBay

Hamfests

www.surplussales.com


There are other surplus houses which carry New-Old-Stock transformers; Google for them. If you're interested in voltages of ~1kv, have a look at some old "CB" amplifiers. Many show up on eBay and @ the local 'fests from time to time. Their transformers can be removed and used to construct a supply for medium-power HF/VHF amplifiers, for example.

Anything bigger (such as a legal-limit amp running 2500-3500v anode potential) deserves a Peter Dahl, Thordarson or similar transformer. These companies will build a transformer to your specifications should you wish.

WB2WIK
10-14-2005, 03:04 PM
Surplus but perfectly good high voltage transformers are very easy to come by, so doing anything "else" seems silly.

I have shelves full of high voltage transformers, acquired over the years at hamfests, from surplus warehouses and also from Fair Radio Sales in Ohio (mail order) http://www.fairradio.com

I would not every apply a higher-than-rated voltage to any transformer winding, it's a good way to start a fire.

WB2WIK/6

K5UOS
10-14-2005, 03:46 PM
A good source for new classic style HV transformers is Hammond. Antique Radio Supply sells them. I buy mine from Angela Instrument on-line. Angela also sells PS chokes.

My opinion (mine only) is that due to the associated risks with high voltage (>360vdc to me) a brand new or NOS transformer is safer particularly if this is a new experience for you . New hardware is not necessarily better than a used transformer but safer and more reliable.

WIK is correct about using a power transformer in a manner not intended. Safety, safety, safety. Three good words to continue to live by. I suggest a good reading of the old handbooks on rectification, filtering, estimating secondary voltage, regulation, fusing, choosing what voltage transformer and rating you need, etc. The reading is both fun and a learning experience. And might insure that sometime in the future you will be around to ask more great questions on QRZ.com.

K5UOS dk

K8ERV
10-14-2005, 04:32 PM
Certainly you CAN apply 120v to a low-voltage secondary. Go for it!! Just be sure you are behind a pane of bullet-proof glass and have a fire extinguisher handy. You are likely to need both. But could be fun. Send a pix.

TOM K8ERV Montrose Colo

KL7AJ
10-14-2005, 07:52 PM
Quote[/b] (K8ERV @ Oct. 14 2005,09:32)]Certainly #you CAN apply 120v to a low-voltage secondary. Go for it!! Just be sure #you are behind a pane of bullet-proof glass and have a fire extinguisher handy. You are likely to need both. But could be fun. Send a pix.

TOM K8ERV #Montrose Colo
You silly boy, you!

Actually, if you put a light bulb in series with the primary, you should only need a fire extinguisher.

Eric

KL7AJ
10-14-2005, 07:55 PM
Quote[/b] (K5CEY @ Oct. 13 2005,18:14)]
Quote[/b] (KD4AL @ Oct. 13 2005,18:52)]Is there any reason that I could not reverse the connections, apply 120vac to the secondary and get 600vac on the other side? #It all uses the same core. The low voltage winding should usually be of a higher guage wire than the primary, since the low voltage side carries more current. #

Bill KD4AL
Bill,

# I'd hate to be in the same room when you try it.

That 24 volt secondary is going to pull a terrific amount of current from the 120 vac wall socket!

May trip the 'breaker and may fry the transformer.

# # # # # John
Actually, we used a reversed "pole pig" for an FM broadcast transmitter when the plate transformer blew out. With 220 in, we got 14KV out....almost precisely what we needed. I don't recommend this for amateur use, though. Unless you're really into QRO.


eric

KA5S
10-14-2005, 08:39 PM
Quote[/b] (kl7aj @ Oct. 14 2005,12:55)]Actually, we used a reversed "pole pig" for an FM broadcast transmitter when the plate transformer blew out. #With 220 in, we got 14KV out....almost precisely what we needed. #I don't recommend this for amateur use, though. # Unless you're really into QRO.
What you did NOT do, however, was apply 14 kV tothe 220VAC side, which is the equivalent of applying 120VAC to a filament winding.

Raise the lightning rod, Igor! The dead (air) will LIVE AGAIN!

Cortland
KA5S

K5CEY
10-15-2005, 05:50 AM
Quote[/b] (KD4AL @ Oct. 13 2005,18:52)]I'm looking to build a high voltage power supply to use with some tube projects. #
Bill KD4AL
Bill,

If you have a specific project in mind that requires a high voltage source, put out your requirements here on QRZ. Myself, I have several hundred pounds of HV and power transformers salvaged from early TV and broadcast sets.

Steve mentioned that he has a whole bunch of HV transformers on the shelf. And knowing Steve, he's probably got several that would power up an electric chair (or a 4-1000A rig--same difference).

For general tinkering, an adjustable supply might be your ticket. Heath and others made some pretty neat 0 to 300 volt supplies. Or, you can build your own with bits and pieces, odds and ends, and back-fed transformers.

Just let us know what you're looking for.

John

KA9VQF
10-15-2005, 05:35 PM
Quote[/b] (K8ERV @ Oct. 14 2005,09:32)]Certainly #you CAN apply 120v to a low-voltage secondary. Go for it!! Just be sure #you are behind a pane of bullet-proof glass and have a fire extinguisher handy. You are likely to need both. But could be fun. Send a pix.

TOM K8ERV #Montrose Colo
and to think that some people say Im sick and twisted,. http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif

K8ERV
10-15-2005, 06:29 PM
Quote[/b] (KA9VQF @ Oct. 15 2005,10:35)]
Quote[/b] (K8ERV @ Oct. 14 2005,09:32)]Certainly #you CAN apply 120v to a low-voltage secondary. Go for it!! Just be sure #you are behind a pane of bullet-proof glass and have a fire extinguisher handy. You are likely to need both. But could be fun. Send a pix.

TOM K8ERV #Montrose Colo
and to think that some people say Im sick and twisted,. # # # # # # # # #http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif
A painter once put his shoes on backwards. Fell off a scaffold, landed on the ground, looked at his feet and reported that he was "ok, but badly twisted". #Actually "twisted" doesn't mean much since the law of parity was shown to be wrong. Twisted lies in the eye of the beholder, or something like that. #I never claimed NOT to be twisted, still trying to figure out if right or left, or something in-between tho!!!

TOM K8ERV #Montrose Colo

K8ERV
10-15-2005, 06:33 PM
Quote[/b] (WB2WIK @ Oct. 14 2005,08:04)]I would not every apply a higher-than-rated voltage to any transformer winding, it's a good way to start a fire.

WB2WIK/6
Right. The way I always start my campfires. Work every time. Just gotta find some more LV Xformers---

TOM K8ERV Montrose Colo

KA0GKT
10-15-2005, 06:56 PM
Quote[/b] (kl7aj @ Oct. 14 2005,12:55)]
Actually, we used a reversed "pole pig" for an FM broadcast transmitter when the plate transformer blew out. #With 220 in, we got 14KV out....almost precisely what we needed. #I don't recommend this for amateur use, though. # Unless you're really into QRO.


I dunno, 14 KV B+ at about 60 % efficiency would be around 1,500 Watts out at with 179 mA plate current.

So, What make and model PA cabinet did you use the pole pig on? #Not a Continental 817A? #http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif # (The 817A was a one tube 60 KW TPO cabinet which never really worked out. #Continental recalled and dismantled all thirteen that they made...perhaps if they had only made twelve or made that fourteenth.)

73 DE KAGKT/7

--Steve

KB2VXA
10-15-2005, 09:14 PM
Hi Bill and readers,

There is much to learn about transformers, start with how windings are phased and how to phase separate but LIKE units (to maintane balance). Next lesson, voltage doublers. A good place to start is a pre 1980 ARRL Radio Amateur Handbook.

When you know what you're doing contact my old friend and ask if he still has any transformers that will suit your purpose. Sorry, no e-mail listed.

WA2EEA
Sidney Wolkin
2311 De Sisto Dr
Rahway NJ 07065-2115
USA

Oh, leave the pole pegs to the power company unless you have a need for 2400V @ ~50A. (;->)

W8ZNX
10-15-2005, 09:42 PM
hello all
Iv used back to back 12 volt transformers
for power supply on small qrp tube transmitters
117 in 6 out - #6 in 117 out
and take fil voltage for tubes from between them

but it was just a expedient
had few dozen of them around just gatherin dust

antique electronic supply wants arm and a leg
for transformers,
#
mid pwr transformers
often cheep and easy to find at swaps
also can tear apart old tube junk nobody wants
often found in the trash at the end of the swap
old basket case tube equpment can be
a wealth of parts

yours truly mac

KC0UUT
10-18-2005, 12:56 AM
=> Is there any reason that I could not reverse the connections, apply 120vac to the secondary and get 600vac on the other side?

Don't do it. Operating an iron core transformer at over rated voltage will cause the magnetic flux in the iron core to saturate. Things will get rather interesting when this happens. The transformer will buzz loudly, the current draw jumps way up which will then trip the house circuit breaker if you are lucky, or set the transformer on fire if you are not. The transformer might tolerate 5 to 10% overvoltage, but not the 5 times overvoltage you are suggesting.

You can operate transfomers at less than rated voltage with no problems.

John

N0WVA
10-18-2005, 01:19 AM
Quote[/b] (KD4AL @ Oct. 13 2005,17:52)]I'm looking to build a high voltage power supply to use with some tube projects. #But I have discovered that high voltage power transformers are very expensive. #Old junk tube parts-radios are getting scarce. Plus a hate to cannibalize anything that might have a chance of being fixed.

It is easy to find decent sized power transformers with 120vac primaries and low voltage secondaries (6vac, 12vac, 24vac, etc.). In fact, I already own one with a 24vac secondary.

Is there any reason that I could not reverse the connections, apply 120vac to the secondary and get 600vac on the other side? #It all uses the same core. The low voltage winding should usually be of a higher guage wire than the primary, since the low voltage side carries more current. #

I would not try it with a 6vac secondary. #I'd rather not deal with 2400vac if I can help it. Although I might use a 120 to 6vac transformer to heat filaments.

Anyone with experience in this?

Bill KD4AL
No, it wont work. The low voltage winding will look like a dead short to the mains.

Get a cheap and readily available line isolation transformer. 120v in -120v out. Then use a voltage doubler. Should get you good voltage for most receiving tubes.

Try googling Burdens Surplus sales. They specialize in hydraulic stuff but also have some electrical.

You could use a doubler on the 24 v transformer you have now and get over 50v for stuff like regen receivers. They should work well on that volatage, especially triodes.

k5gx
10-25-2005, 06:12 AM
Hi:

Looks like I'm about 7 days late, but maybe this will help somebody.

Xfmr's have a polarity, known as instantaneous polarity. On a schematic that shows instantaneous polarity, you will see a small dot at the end of each xfmr winding, whether it be a PT (potential xfmr) or CT (current xfmr).

If you apply 120vac to a 120vac xfmr primary, you can add on additional xfmrs that are rated for 120vac, wired in series with the 1st xfmr. It's called an auto-transformer. The secondary windings are not even used (but can be). The primary windings must be capable of handling the total current load though (pri & sec windings). In ac, I x E = VA. If your smallest rated xfmr is rated for 60va, then the max current is 0.5 amps.

Example: label the primary leads on 3 each xfmrs, a-b, c-d, and e-f. Connect leads b to c, and d to e. Connect 120vac to a and b leads; the result should be 360vac between a and f leads. If not, check polarities of each xfmr. For example, reverse c and d, or e and f leads.

Just remember, this will be like the old tube radios that didn't use a step-up xfmr--there is no isolation to protect the user, should that person contact ground or even the 120vac hot wire if the potential is different. Be especially careful of the 360vac potential to the neutral or ground.

I'm sure I didn't word this too well--it's been a long day and I'm really tired. Be sure to de-energize any circuits before reversing any leads, and I'd recommend fusing at 1 to 2 amps to protect your xfmrs. Also, if you could get your power from a GFCI outlet, this could certainly help protect you!
Wish you well. Bill 73's K5GX

AB6ND
10-25-2005, 06:37 AM
I'll bet you will find plenty of old tube type TV sets in garage sales. I saw two this weekend. The power transformers in them are excellent. Make sure it's not one of the really old models ac/dc !
Use solid state diodes instead of the usual 5U4 rectifier tube and you can draw all sorts of voltage from them. Also if you want to make use of the 5U4 winding you can "boost or buck" by phasing and have some control over the voltage.
AB6ND

K8ERV
10-25-2005, 08:30 AM
Basically a transformer does not know or care in which direction the power flows. There is no real difference between a step-up and a step-down design, so long as no windings see more than their rated voltage and current.

There is a general rule-of-thumb that a simple class A open-frame transformer can support a total of 20 watts/pound.

TOM K8ERV #Montrose Colo

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