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Author Topic: SUBSTITES FOR 30L-1 METER AND POWER TRANSFORMER AND POWER SWITCH?  (Read 3951 times)
N6QWP
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« Reply #60 on: September 17, 2018, 08:27:53 PM »

Oops.....I think I see what threw me waaay off the track.  I understand two tubes at 12.6 each getting 6.3 and the current will still be the same if the two are in series.

What I thought I read, was the comment about "even 20" would all receive 4 amps?  Upon re-reading, I don't think it applied to the same supply of only 12.6 volts.....AT LEAST I HOPE NOT!

Perhaps that is what has stalled my comprehension of this issue.

If G3RZP can kindly straighten me out on this issue, I think that this issue will finally be understood?
....
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G3RZP
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« Reply #61 on: September 18, 2018, 06:02:30 AM »

20 tubes would require 126 volts. You have to apply Kirchoff's law about the current adding up around the circuit to zero. In the days of analogue repeaters on submarine cables, they used to feed quite high voltages in from a constant current supply: each repeater drew substantially the same current and so ended up with right volts across it. Bear in mind that TAT1, the first Transatlantic Telephone cable used tubes with over 51 repeaters at 69km intervals: it opened in 1956. Incidentally, my father in law worked at the HF station at Rugby: he told me that when TAT1 opened they took some 18 HF ISB telephone channels out as no longer needed and had them back again within three weeks because of the increased demand!

Some of the signalling systems on railways in the UK also use constant current sources with things in series.

Many of 'All American Five' tube radio used series heater strings: a 12K8, a 12K7, a 12Q7, a 35Z5 and a 50L6, all with 0.15 amp heaters, adding up to 112 volts and connected across the 115 volts supply of those days. That saved the cost of a mains transformer....
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KM1H
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« Reply #62 on: September 18, 2018, 07:24:03 AM »

Quote
Many of 'All American Five' tube radio used series heater strings: a 12K8, a 12K7, a 12Q7, a 35Z5 and a 50L6, all with 0.15 amp heaters, adding up to 112 volts and connected across the 115 volts supply of those days. That saved the cost of a mains transformer....

You really are showing your age Peter!  The more common octals are the 12SA7, 12SK7, 12SQ7, 35Z5, 50L6. These days a 45Z5 is a popular swap for the higher line voltages.

Carl
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N6QWP
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« Reply #63 on: September 18, 2018, 09:31:33 AM »

Thanx Guys!  Finally got through to what is left of this old brain matter.
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G3RZP
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« Reply #64 on: September 19, 2018, 04:17:07 AM »

Carl,

Of course I'm showing my age! I went to my first FD in 1948 in a stroller at the age of 13 months.....Definitely brought up in ham radio.

The 12SA7- 12SK7 -12SQ7 line up never caught on over here - standard before miniature valves was 12K8 - 12K7 - 12Q7 - 50L6 - 35Z4, with a dropper resistance to allow for 240 volt mains. A very few radios used line cords..

73

Peter G3RZP
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KM1H
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« Reply #65 on: September 19, 2018, 09:24:49 AM »

I wasnt aware of that lineup in the UK Peter.

By '52 (born in 40) I was crawling around local town dumps and tossing discarded radios into bicycle paper delivery bags and side baskets and building non ham specific magazine projects and by 54 had a AA5 style 5 tube regen operating. By 55 I knew enough CW and entry level theory to pass the Novice the first time and built a 6AG7-6L6G TX for 80/40 plus PS.

Before the AA5 the 30's AC/DC sets used curtain burner line cords. I have several in the collection for display only! Grin

Carl
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N6QWP
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« Reply #66 on: November 16, 2018, 07:36:12 PM »

Just purchased a 0-500 uA Russian meter that is supposed to fit the hole in the 30L-1 as a replacement for $17 (on epay).  The scale reads that....just hope that it is the actual current rating.

Not holding out too much hope, but might work temporarily and the price is right.  Figured it might work "close enough" for reading the voltage and current (by multiplying the readings by 2 and by 4).  At least, I hope that I should get some useful relative readings for tuning.

Not using the Collins quick tuning procedure that uses the down reading part of the scale, so crossing my fingers and hoping for the best.

Been searching for a real Collins replacement meter....but haven't been able to find a "deal" that I'd want for an old amplifier "abortion".  This old project is loafing along at a snail's pace....but getting closer all the time.

Found (what I think is) an old  Heathkit cabinet that "almost fits" and looks pretty close to the original Collins.  Need a couple more pieces of metal work to safely button up the unit, and it should be ready to test out to see if it will perform as a good "final" test platform for the old 811 and 572 tubes.....maybe even get on the air at some point?

Love tinkering with this old gear.  Have a couple of nice 30L-1's and this "basketcase of the living dead".  It's amazing what a little determination and some insightful and knowledgeable help from this forum can accomplish.  "Never abandon the really good old gear".....just keep it keepin on....even if it's with bandaids and chewing gum.

Thanx to all that helped and very 73's.
« Last Edit: November 16, 2018, 07:58:43 PM by N6QWP » Logged
G3RZP
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« Reply #67 on: November 17, 2018, 12:35:33 AM »

If you open up the meter and can get to the rear hairspring, you may be able to move the part it is attached to such the that meter with zero current is offset up the scale, thus giving you the equivalent of the Collins meter. You could then make a new scale from thin card or even paper stuck over the original. Relatively easy to do with a computer - in the old days, we used a draughtsman's springbow and Indian ink!
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N2EY
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« Reply #68 on: November 17, 2018, 07:59:47 AM »

Bear in mind that TAT1, the first Transatlantic Telephone cable used tubes with over 51 repeaters at 69km intervals: it opened in 1956. Incidentally, my father in law worked at the HF station at Rugby: he told me that when TAT1 opened they took some 18 HF ISB telephone channels out as no longer needed and had them back again within three weeks because of the increased demand!

There are documentaries about TAT1 and successors on youtube:

https://www.youtube.com/watch?v=QVRL4UcT1sQ

https://www.youtube.com/watch?v=qOg3aWwE_a0


Many of 'All American Five' tube radio used series heater strings: a 12K8, a 12K7, a 12Q7, a 35Z5 and a 50L6, all with 0.15 amp heaters, adding up to 112 volts and connected across the 115 volts supply of those days. That saved the cost of a mains transformer....

Yes - also reduced the size and weight, which brought additional savings in storage and shipment.

In addition, properly-designed transformerless radios could be used on 100Hz, 60 Hz, 50 Hz, 25 Hz and DC mains without modification.

73 de Jim, N2EY
« Last Edit: November 17, 2018, 08:05:18 AM by N2EY » Logged
N6QWP
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« Reply #69 on: November 18, 2018, 07:33:01 AM »

G3RZP-Tnx
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KM1H
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« Reply #70 on: November 18, 2018, 08:09:36 AM »

Good information as always Peter.

Carl
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W1QJ
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« Reply #71 on: November 20, 2018, 05:45:36 AM »

If you open up the meter and can get to the rear hairspring, you may be able to move the part it is attached to such the that meter with zero current is offset up the scale, thus giving you the equivalent of the Collins meter. You could then make a new scale from thin card or even paper stuck over the original. Relatively easy to do with a computer - in the old days, we used a draughtsman's springbow and Indian ink!

Pretty much what I do when I make up my clone Kenwood TL-922 Ip meters.
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N6QWP
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« Reply #72 on: December 05, 2018, 01:53:12 PM »

Well, the 0-500uA meter that I ordered from Russia just arrived.  While the four holes for the mounting screws are a bit too small, with a bit of drilling them out, it'll be a perfect fit.

The 0-500 scale will be easy to multiply for voltage and current.....if the scale readings are close.  Guess that will depend upon the internal resistance of this meter.  

Crossing fingers, but in actuality, the meter will only be used for reference.  Will be using an external power swr meter to tune up the amp if it ever gets to the point of functioning in that capacity once again.

Doesn't look like it can be taken apart very easily to move the zeroing resting point or to replace the meter face, but that is not of concern.  Looks great!  (And the price was right!).

Since this whole project is just a "Collection of Close", it is continuing on.  Still need metal work, cages and various other parts, but since the goal is to get this "working" for Very Little investment, am well on the way.

With a few more parts and getting it to the point where it can be safely buttoned up (without worrying about electrocuting myself), I hope to be able to run some tests on old 811's before too long.
« Last Edit: December 05, 2018, 02:13:03 PM by N6QWP » Logged
N6QWP
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« Reply #73 on: December 05, 2018, 06:01:51 PM »

Actually had to "drag" the holes for the four mounting screws on the meter, out with a drill bit....about 1/16' to 1/8".  Meter now fits perfectly and the holes do not show outside the meter.  The diameter of the meter hole itself was fine.

I found an original Collins 30L-1 meter for $50, but figured that, since this was an experiment, would wait and see if this Russian meter would fit.  Happily, it does and should work just fine for what I need.

With the "Heathkit" cabinet and the Russian meter, it now looks pretty presentable....very close to original.  At least, it now looks professional and not the "hackjob" that it really is.  Now on to searching for the missing chassis metalwork pieces so that it will be rigid, rf tight, safe and "semi- complete".

PS--After all this, I would DEFINITELY NOT recommend anyone else trying to "resurrect" a basketcase 30L-1.  Finding the necessary pieces is waaaay too time consuming and costly if trying to bring one of these amps back to "original".

Howsomever, if you are a bit "out there", have nothing but time to kill, and "enjoy the hunt"....it definitely is an interesting endeavor....at least if NOT too concerned with anything other that it "perhaps working".

Hopefully, I will still end up with something better than a similarly priced "homebrew backyard" project amp.  At least the basic chassis, panel and layout is already done....and it will look like a "real amp".
« Last Edit: December 05, 2018, 06:25:57 PM by N6QWP » Logged
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