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Author Topic: Collins 32V audio mod problem  (Read 24619 times)
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Steve - WB3HUZ
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« Reply #25 on: October 04, 2009, 01:10:12 PM »

The screens could be at risk, but since the LV and HV operate on the same switch, the operator could never cause the problem. If the HV supply craps out, you have a different story. These mods have been done by many  people and I've never heard of this problem. That said, there is a possibility. Like any mods, there is some risk involved.

If you would like to submit improved mods, please do so. It would be greatly appreciated. They will be added to the collection or be used to replace older, less complete ones.



I just looked at another modification at amwindow.org, and this one is for the Viking II. Take a look at the circuit:

http://amwindow.org/tech/htm/vikinga.htm

So what is wrong here?

1.) negative feedback is eliminated with 6C4 cathode bypass capacitor (might work fine without NFB)
2.) If the 807 screens are tied to the low B+ as in note 1, won't the 807's screen grids burn up when the high B+ is turned off??
3.) ??

Maybe add a second note to key the screen grid of the 807 with a relay??

I realize that folks went through a lot of trouble to come up with these modifications, and again to document them and post them. I applaud this effort. I do hope though that folks contemplating any of these modifications realize that these posts are not necessarily complete. Therefore, ask questions on this forum first, and hit a book or two before warming up the soldering iron.

Regards,
Jim
WD5JKO
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Steve - WB3HUZ
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« Reply #26 on: October 04, 2009, 11:42:10 PM »

Nice catch guys. The mod info has now been modified. The Note 1 section has been removed.

Thanks for your input. We don't need to be burning up any 807s needlessly.   Grin
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W3SLK
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« Reply #27 on: October 05, 2009, 09:07:36 AM »

Steve said:
Quote
Thanks for your input. We don't need to be burning up any 807s needlessly.


Oh the humanity!!!!!  Cry
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
Todd, KA1KAQ
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« Reply #28 on: October 05, 2009, 06:16:34 PM »

that cap looks like some attempt to resonate the choke. the minute you change the other values, it''s probably way out of resonance hence the blowing up. That cap would only work in a bone stock rig.

Interesting point, Derb. Though nothing in the set has been changed or modified, it got me to wondering if a few shorted turns in the choke may be the culprit. It's munched a couple of original .25 mfd 2kv oil units in short order. Found an exact (but taller) 5kv unit at Shelby and installed it, so far no issues. Applying the old principal 'If it doesn't work, force it. If it breaks, it needed replacing anyway'.  Grin

Back to the issue of hum. Hmmmmmmmmmmmmmmmmmmmmmmmmmm. Got me to thinking of an issue I had with an old Zenith set years ago. Since the issue developed after operator intervention for mods, I'm wondering if it's a simple case of inadvertent installation or repositioning of a component or line near a source that it wasn't near before. This happened to me with the old Zenith set, changing caps and repeated revisits produced no improvement. Then I accidentally moved a wire added by a previous owner for phono use, and noticed a difference. A little experimenting with repositioning and voila - hum gone.

Seems like the problem has been addressed in the subject 32V, but still a good thing to remember. Sometimes it's the obvious things we miss looking for something more worthy of being called difficult.


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known as The Voice of Vermont in a previous life
N3DRB The Derb
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« Reply #29 on: October 05, 2009, 09:09:56 PM »

Quote
Sometimes it's the obvious things we miss looking for something more worthy of being called difficult.

I kinda specialize in that these days.  Undecided I dont work on things logically anymore, but more on emotion.
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Gito
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« Reply #30 on: October 05, 2009, 09:48:16 PM »

Hi

I agree with W5HRO,since the feed back is taken from the HV power supply,secondary winding of T202/mod.trafo ,the hum can be introduced from this supply ,because if the supply has a little ripple/hum it is amplified by the 2ND (V201) and the modulator.

When we changed a tube rectifier with solid state rectifier ,

the tube rectifier takes time to rectified the ac voltage because it needs to get "warm" to conduct ,so the in rush current is not high,

with solid state rectifier ,when you switch on the transmitter ,it directly conduct ,so the in rush current is high ,that makes the fuse open.
with higher value of C the inrush current is higher.

Try to change or parallel C 303 with a higher value of C ,the more higher the less ripple of the HV supply.
Still used the tube rectifier .

When using Solid state rectifier ,we must used surge limiting devise in the primary winding of the HV power supply.To limit the inrush current

Gito


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N2DTS
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« Reply #31 on: October 05, 2009, 10:50:11 PM »

Well, in the case of the 32v, the high voltage is keyed on transmit, vacuum rectifiers should be conducting by that time.
The low voltage power supply is on all the time, but on power on, there is almost no load as none of the tubes have warmed up yet.
Both supplies are choke input, so surge current is fairly low, even with big caps.

The cap across the choke was a popular method to improve regulation, its in the Bill Orr handbooks.
I have never had a problem with mine, and even added a .5uf across the choke in my big rig supply.

I have run the 32V3 up to 900 volts on the B+, I have my 32V3 rack mounted, and was using it as an rf exciter for the big rigs, and used the variac as a 'dial a power' knob, its mounted on a rack panel in the bottom of the rack.

As a standalone transmitter, I usualy run it about 800 volts and 180ma, it seems to modulate better that way.

This 32V3 I got as one of two for $90.00, both looked like new, one blew the LV fuse, and the seller thought the LV transformer was bad, but it was a shorted trimmer cap in the multiplier section...

I also had a 32V1, and never had any problems with any of them except one had the plate tuning cap arc over all the time because there was force on it shoving the plates off center, an easy fix.
All had been solid stated without any dropping resistors and run on the 700 volt tap.

Of all the 'ham' gear I have had over the years, its the only thing that has stayed in the shack for 30 years.
A well built transmitter!

Brett

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