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Author Topic: CHC46140 aka RBG 2 aka HQ120X aka Hq129x  (Read 1001 times)
G3RZP
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« on: September 04, 2018, 02:23:47 PM »

It appears that the CHC46140 was a modified HQ120x or HQ129X to band spread the HF marine bands rather than the amateur bands. How rare is it in the US and any idea of possible value? It appears to be pretty rare over here....We have been offered one, possibly for free, if we hurry and save it from the dumpster. Otherwise, we are wiling to sell at one of our auction for 15% of the sale price. I'm figuring that it might fetch $100 here but I could be wrong....

vy 73

Peter G3RZP
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KM1H
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« Reply #1 on: September 04, 2018, 03:19:46 PM »

I own one Peter. They were built for the US Coast Guard during WW2 and are much closer to the HQ-129X than the 120. Note they also used the 6SK7 in the RF and IF instead of those dead 6SS7's in the 129 which were the first changes I made to my first one in 1956!

Carl
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G3RZP
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« Reply #2 on: September 05, 2018, 01:43:46 AM »

Tnx for the info, Carl.

How much do they generally sell for? Not the usual crazy eBay price, of course!

What was the problem with the 6SS7? The characteristics look pretty similar to the 6SK7, except for the lower heater current - which could lead to a shorter life maybe?
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KM1H
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« Reply #3 on: September 05, 2018, 11:46:41 AM »

The lower heater current results in less reserve emission and the transconductance is the lowest of octal AGC controlled pentode RF amps...its a dog and reportedly a misguided attempt to improve overload handling.

The miniature 6DC6 was another dog that Collins fell in love with....in the R-390A it "may" have been beneficial due to the nature of the use of those radios. OTOH in the 75A3 and A4 it probably resulted in the:

"If you want a frequency meter buy a Collins, if you want to hear them buy a National"

Hallidrifters did the monkey see monkey do on a few sets.

Carl
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G3RZP
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« Reply #4 on: September 06, 2018, 06:15:37 AM »

Carl,

Did the same emission problems exist with miniature 6BH6 and 6BJ6 and with the 175mA heater 717A?
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KM1H
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« Reply #5 on: September 06, 2018, 05:41:30 PM »

I dont know the life of the 717A which is a 6AK5 on its side. In the 50's I was swapping between it and a 6SG7 with the 717A used on 10M of a HQ-129X where the poor AGC action didnt matter much.....even during Cycle 19.
These days I use a 6SG7 in the RF and first IF and rarely go past 15M.

Watch it with glass tubes as the grounded shell pin for the metal tubes is often used as a B+ tie point.....I learned that in the 50's Roll Eyes

Ive little experience with the 6BH6 and the 6BJ6 as used in the NC-300/303 IF's often tested weak.....all tubes were tested at National and weak ones (usually originals) were replaced even if it didnt make any difference in performance. I dont believe I replaced them in my 300 or several customer sets as the full radio most always tested at a .2 to .25uV 10db SNR on 10M AM. There was no equipment or cable leakage. Even my favorite 6GM6 swap made only a little difference on the meter and none that I could hear.

Carl
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