How do I protect the LV transformer in my 32V3 ??

[N2IDU]

I have a stock 32V3 which is in fine shape both electrically and cosmetically. I would like to use it on a long term reliable basis as my main station.  I understand that the 32v's series suffer a weak link in the low voltage transformers. I have already installed a Bi-directional voltage suppressor & a mov oxide varistor across the ac line as described  in K1deu's web page. I have a solid state rectifier to replace the 5z4 but am unsure if this would hasten a premature failure. In addition, I am considering an "inrush current limiter" but don't know what value to use.

Any suggestions, pointers or comments would be greatly appreciated.

Thanks,

Peter N2IDU  Old Shincracker Vermont

[w8khk]

Hello Peter,

I have two 32V2s I am restoring, and I completed restoration of a 32V3.  I decided not to replace the 5Z4 with a solid state rectifier, because the 5Z4 uses an indirectly heated cathode, which delays the B+ until the other tubes have heated, thus limiting the soaring of the B+.  Also, when running solid state instead of the hollow rectifiers, peak current on the transformer secondary is greater, which will likely cause more heating.  Solid state is not always better than the tube rectifier, and the ten watts consumed by the 5Z4 heater are inconsequential.  In all the time I have run the 32V3, the LV power transformer does not even get warm to the touch. 

It might be more prudent to replace the HV rectifier tubes with solid state, eliminating the filament load on the LV transformer.  Only one solid state rectifier is required, because the two tubes are in parallel.  But make sure your replacement can handle the total load of the final and modulator, as well as screen supply.  If you use solid state for the HV, you might consider running the HV in 600, rather than 700 volt mode, as the solid state rectifiers will have less voltage drop than the hollow state originals. 

While the whole rig runs rather cool when not in the cabinet, there is not a lot of air flow when it is enclosed.  Make sure there  is plenty of space around the cabinet for convection, or add some circulation with a small muffin fan.

73,
Rick

[WA1GFZ]

Many old rigs were set up for 110 vAC input and the transformers are near saturation at 125 volts. My line is up around 126 volts most of the time so I put both 5 volt windings in series with the primary of my V2 transformer and added a fuse to the primary mounted in the 6AL5 bias rectifier tube hole. My heater voltage dropped from 6.7 to 6.25.VAC. The transformer use to run very warm even in stand by. Now there is barely any temperature rise.

[W3RSW]

Did the same thing Frank.  Many postings on this site over the years showing boost/buck lashups.  In my case I had an extra 10v/20a fil. xfor that I rigged up in buck mode to get 120v in and 115 out. I run both the 32V and 75A2A off same output.  I just mounted a metal outlet box on the upside down fil. tranny that has a couple of plugs and covers up all the posts and wiring.  I put rubber feet on the 4 fil. xfror top cover mounting holes, (now upside down) Yes, All the Collins lit. for 32v shows it 'want's 115vac.   My house voltage seems to be pretty constant at 119 to 121 volts AC RMS.

Also solid stated both HV and LV rectifiers in my 32V2.-  Put 470 ohm, 2w paralleled w/ 0.1uf/600v across lifted and unused 5 v. winding. Just felt better that way to give it a tiny load.

Didn't see a whole lot of diff. in B+ voltages from bogey  ... must be some leaky bypasses on screens, etc. ....      - but at any rate no loss in output

[WA1GFZ]

Using an extra transformer gives you more loss. Also there is no problem floating a low voltage winding. At 119 to 121 volts you would only need to series 1 5 volt winding.

[k7yoo]

There was a good article in ER several months ago regarding replacement of the unobtainium 32V LV transformers. It discusses the technical merits of much of the current thread on this topic. My personal experience in running a 32V1, 2, 3 for the past 30 years is this:
run SS rectifiers in the HV, buck the line voltage back to around 117. Doing only these "fixes", I have only lost one screen resistor (corrosion), and a couple of mica caps in the output tank (high SWR).
I do not like the LV rectifier, as they are not very robust and can take out the transformer if a short develops. The benefits of SS may outweigh the negatives.

[W3RSW]

-forgot to mention that the primary of the 10v fil. xfor is nominally 230v. 

[Todd, KA1KAQ]

Having just recently gotten my 32V-2 back from WA2PJP, I recall we read the specs in the manual to say that power input was 120VAC +/- 10% or something to that effect. So unless your line voltage runs high, it shouldn't be a problem. Mine hovers around 120, up from 117 a couple years ago.

Simple but crude: make a small shield out of alfoil and place it between the transformer and 5Z4, shiny side facing out. Bend to suit. IMO, the radiant heat caused by that tube is far worse than any increased heating from elevated line voltage. It sits maybe 1/2" away from the side of the transformer end bell, and it is HOT.

Probably wouldn't hurt to hang a small muffin fan on the back grill as well, sucking heat out. This should pull cooler air in through the side cabinet handle opening, right next to the tube and transformer. Run some insulated wire through the screw hole mounts on the fan and just hook in through the louver slots - no drilling or paint damage required.

And if you do lose the transformer at some point, keep WZ1M as well as the company who took over Dahl's name in mind as I'm sure they can both rewind it for you. Today's insulation is much better stuff, and I've seen Gary '1M's work firsthand. He uses Nomex and a variety of other materials in the rebuilding process that should provide a very stout transformer for decades to come.

[W3RSW]

My manual, labeled 2326 bottom right of page 1-2 for the 32V3 states 115vac 50/60cycles, single phase.  Max power at 500 watts at 90% power factor.

Same thing in my 32V 1 manual, 4/14/48, page 1-2 ; 14194-2.

As Frank notes, The 6.3 ac filament line seems to be a good indicator being independent of hi/lo HV settings, cap. leakages, etc. Mine dropped from about 6.6 to 6.3 also after dropping to 115 vac supply.

[W2JBL]

 been running my 32V2 since 1972 with solid stated power supplies and no other real mods except basic ones in the speech amp. average line voltage here is 126. never had a problem other than a wandering PTO a few years ago. no need to put two condoms and 17 surge suppressors on a 32V before getting on the air...you guys worry too much about this S#$T. put it on the air. if it breaks (unlikely) then fix it and get back on. if you are too scared to do that then shrink wrap it and put it on the shelf.

[W3RSW]

Yeah, I solid stated (no ballast r's either) my HV and LV too. Lifted the 5v winding
I agree it is one strappin' rig and can take a lot of abuse but just felt that 6.6v + on the 6.3 string might affect all the pubes over years.  I'd run the damn things at 5.9 or 6.0 volts, cept' maybe for a doubler or two and the xmit final/mod. tubes if I thought I could get away with it.  Besides it was fun to use a Raytheon 220v/10v,20A xfor. in the shack just to try out the buck concept.

This here is a fun hobby

[N2IDU]

Thanks for all you advice and suggestions on the above captioned question. It was sincerely appreciated.

73
N2IDU "Old Shincracker Vt."