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Author Topic: SUBSTITES FOR 30L-1 METER AND POWER TRANSFORMER AND POWER SWITCH?  (Read 4584 times)
G3RZP
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Posts: 1286




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« Reply #15 on: August 29, 2018, 09:20:22 AM »

Since 811As draw 4 amps of filament current, 11 amps seems more than little inadequate for 4 of them. Are Peter Dahl transformers still available after his death some years ago?
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W9GB
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« Reply #16 on: August 29, 2018, 10:30:44 AM »

Since 811As draw 4 amps of filament current, 11 amps seems more than little inadequate for 4 of them.

Are Peter Dahl transformers still available after his death some years ago?
YES.
Peter Dahl shutdown his company in December 2007, due to poor health.
Peter Dahl, K0BIT (sk) died in 2011.

Jeff Weinberg, owner of Harbach Electronics (Ohio) acquired the knowledgebase and handled orders for Peter Dahl transformers (2008-2012), used in amateur radio equipment.
https://harbachelectronics.com

In February 2013, Peter Dahl’s database, brand name, and trademarks were acquired by
Hammond Transformers (Guelph, Ontario) from Harbach Electronics.
http://www.pwdahl.com

You may not be aware that in August 2013, Peter Dahl’s original database server failed.
Hammond started a DATA RECOVERY process to save the Peter Dahl knowledgebase.
http://www.pwdahl.com/PWDnews.html

In 2015, Hammond engineers, using their latest manufacturing and production knowledge, went back and “re-freshed” or “redesigned” the HV transformers (Hypersils) for the Alpha 91β , Alpha 99, and the Heathkit SB-220 HF Amplifiers.  
Dennis, N9AD and Mike, K4VJ served as Beta testers of these new designs.
« Last Edit: August 29, 2018, 10:49:50 AM by W9GB » Logged
G3RZP
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Posts: 1286




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« Reply #17 on: August 29, 2018, 02:14:53 PM »

'9GB,

Tnx for the info. I only ever took passing interest since the shipping cost to the UK would be a problem, especially with import duty and VAT, and even more so with current weak £/$ ratio.

But I still think the 11 amps for the filament winding is insufficient! It needs to be centre tapped, too, for the 30L1.
vy 73

Peter G3RZP
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K6AER
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« Reply #18 on: August 29, 2018, 02:57:53 PM »

Transformers supplied for the Alpha amplifier designs were made by:

Tranex Inc

2350 Executive Cir,
 
Colorado Springs, CO 80906

(719) 576-1503
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N6QWP
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Posts: 740




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« Reply #19 on: September 03, 2018, 07:24:21 PM »

I think that I have decided to use an old TV or stereo amplifier HV power transformer, along with separate filament and bias transformers and adapt this "testing platform" to testing only a single tube at a time.

That way, I hopefully can find old cheap transformers and not risk an expensive one to flashovers during testing of the old 811, 811A tubes.

I am hoping that I can use most of the original 30L-1 circuitry and parts....just downside the available voltage and current to handle one tube at a time.

I just can't justify risking an expensive transformer just to check for gas and flashovers.  I assume that with a 4 amp or better filament supply...and  500-600 volt light duty HV transformer, I can develop enough of the required supply to do an adequate job of testing a single tube?

Using separate transformers, I should also be able to apply the high voltage that is developed incrementally from using a variac in it's primary.

Anyone foresee a problem with using the original power supply capacitor and diode boards with a light duty power transformer to develope the necessary supply to test a single tube at a time?  Any ideas or critiques greatly appreciated.
« Last Edit: September 03, 2018, 07:46:11 PM by N6QWP » Logged
G3RZP
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« Reply #20 on: September 04, 2018, 12:36:13 AM »

There's a reasonable chance that the capacitor board isn't useable with the original caps, as they will probably have dried out with age, although I have electrolytics in use in gear that are over 50 years old. A lot depends on how hot an environment they have worked in.

If you can find an old tube TV transformer giving around 350-0-350 at around 200 mA, that would suffice for one ore even two tubes with a voltage doubler. The original diode string was of 600 piv rectifiers and you could use a string of new 1N5408 1 amp 1kV piv diodes for less than the price of a beer! Plus you wouldn't need thee qualising capacitors.
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N6QWP
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« Reply #21 on: September 04, 2018, 07:41:37 AM »

I have already ordered new caps and diodes from China for the old boards for around $13 (220 ufd @450 vdc's and 1N5408's).  Could you please clarify what you were saying about not needing three "qualising" caps?

Heading to a ham swap in a couple of weeks to see what I can find in transformers, meters and power supplies.
« Last Edit: September 04, 2018, 07:47:06 AM by N6QWP » Logged
KD0REQ
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« Reply #22 on: September 04, 2018, 08:06:36 AM »

in the old days, when blacksmiths forged semiconductor junctions one by one (well, sorta), rectifiers were rather unmatched. so the best one in a string failed and the rest followed. the workaround was to put 470K resistors and .01 disc caps across every rectifier in parallel.

nowdays, with the precision in wafer production and production, plus the larger size, scads and oodles of rectifiers come out of the cut almost exactly equal. practically you can avoid curve tracing and breakdown testing and parallel RC equalization, and just solder the string of rectifiers together.  and they're pennies apiece instead of one to two bucks.
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G3RZP
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« Reply #23 on: September 04, 2018, 11:54:28 AM »

It is however advisable to obtain diodes from the same batch - usually that happens if they are on the same bandolier.
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N6QWP
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« Reply #24 on: September 04, 2018, 12:23:20 PM »

G3RZP-Still unsure of what you are referring to in your earlier mention of 3 qualising capacitors???  Is that a misspelling?  I can't decipher it.  Thanx
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G3RZP
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Posts: 1286




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« Reply #25 on: September 04, 2018, 02:32:10 PM »

You need to talk to the Old Timers at the  local ham club, - that gives you a chance of a power transformer from an old colour TV tube that will do!

Never underestimate the power of scrounging, especially if you are willing to put in some physical effort with an OT's antennas!
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N6QWP
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« Reply #26 on: September 04, 2018, 03:36:14 PM »

I'm pretty good at scrounging.  I've found best sources to be at rare swap meets...and epay as a last resort (if in a hurry).

STILL WANT TO KNOW WHAT YOU WERE REFERRING TO AS "3 QUALISING CAPACITORS"Huh
« Last Edit: September 04, 2018, 03:41:29 PM by N6QWP » Logged
G3RZP
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« Reply #27 on: September 05, 2018, 01:35:02 AM »

When you put capacitors in series and apply DC, the voltage is distributed across the capacitors in inverse proportion to the capacitances, so the lowest capacitor gets the higher voltage. When you have a string of diodes in series in a rectifier chain, the PIV across each diode will be determined by the various diode capacities. Plus any spikes on the supply can cause trouble. In the early days of silicon diode usage, it was usual to place a resistor across the each diode as well as a capacitor so that the reverse leakage inequalities and inequalities in diode capacity under reverse conditions was forced to be pretty well equal for each diode. The 30L1 only uses capacitors of 1000pf across each diode, and no resistors. So that's what is meant by 'equalising capacitors'.

By the 1980's, most manufacturers had processes well enough controlled that this became unnecessary, especially with the advent of controlled avalanche diodes, which these days, most rectifiers are. The main point is that although 'mix n'match' may work with diodes from different batches, it may not, so it's always advisable to use diodes from the same manufacturing batch. Diodes from different manufacturers can have different characteristics - an example is the 1N4007 from Motorola, which had a maximum  trr (reverse recovery time) of about 7 to 8 microseconds, allowing it to be used effectively as a PIN diode in an RF switch. Some other makes of 1N4007 - introduced later - the 1N4007 has been around a long time - had a much lower trr. Not a problem in a power supply - even a good thing - but made them useless an RF switch.

You sometimes find capacitors across rectifiers in receivers. Where a broadcast or HiFi receiver is used in an area with fairly high field strength from an AM broadcast station, you can get RF coupled in from the power line and rectified in the power supply leading to the background AM being there all the time, sometimes with a 50 or 60 Hz hum added.
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N6QWP
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« Reply #28 on: September 05, 2018, 10:52:54 AM »

OK....got it.  There was no "e" and I couldn't make out what you might have been referring to.  The diodes from China, along with the electrolytics, all seem to be from the same manufacturer, but I have no way to determine if from same production runs.  Seems somewhat likely....guess that I will have to try them.


So, Peter, would you check and replace any of the caps across the "new" diodes on the original supply board?  And when you said "when using the substitute tv xfmr, I could eliminate THREE equalizing caps", which ones were you referring to? (When testing single 811's in the test platform).

Or, would you eliminate the caps altogether and perhaps used resistors?  I notice that the newer replacement boards seem to use that configuration.  I'm sure glad that you have enough understanding of both the 30L-1 and the different power supplies.  Thanx again.
« Last Edit: September 05, 2018, 10:55:35 AM by N6QWP » Logged
KM1H
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« Reply #29 on: September 05, 2018, 11:15:02 AM »

Caps havent been needed across modern PS diodes for decades altho they still show up in vintage designs. A single 2000-5000 pf cap of sufficient voltage from the HV output to ground is a good addition for any RF floating around.

A similar cap can be used in SS audio circuits to eliminate the switching harmonics.

My own 811/572B tester is a Dentron 160-10L basket case which can be switched between either voltage requirements. At $50 it was far cheaper than building something.

Carl
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