RCA 6973

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RCA 6973

Postby msmpe » Mon Aug 24, 2009 2:16 pm

Hi all - Is there an equivalent to the RCA 6973? Different pinout is OK, but similar specs.
8>) Mike

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Postby Ty_Bower » Mon Aug 24, 2009 2:42 pm

5CZ5 or 6CZ5?

Maybe not similar enough, but still in the ballpark:
6DL5, CV8458, EL95?

Maybe octal based 6EY6 or 7EY6?

Maybe the circuit could be adapted to fit a 6V6 or 6AQ5?

What's the intended use?
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Postby EWBrown » Mon Aug 24, 2009 6:54 pm

6CZ5 and 5CZ5 are your best bets. Pinout is similar, but not exact. They should work fine in the RCA tube manual 15W 6973 amp circuit, as the plate voltage and currents are relatively "mild" for these tubes.

12AB5 has the same pinout as 6973, and characteristics similar to 6V6GT
except for teh 12V filament. OK, howzabout a 12V6GT or 12AQ5 for that one... .

Actually fir most intents and purposes, the good old EL84 and its many varioants are generally "close enough".

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Modern Production

Postby Gingertube » Mon Aug 24, 2009 10:05 pm

Electro Harmonix do a modern production 6973. I just bought a matched quad from the local EH agent. Haven't fired them up yet so don't know how they will sound.
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Postby EWBrown » Tue Aug 25, 2009 3:09 pm

Thanks! I was wondering if there was a Russian new production 6973 (or equivalent).

Given that, I wonder if they are really copies 6973s, or just re-configured 6P14Ps (???)

Someday I'll have to get a quad of EHs and run them in a "shootout" against my NOS RCAs.

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6973

Postby msmpe » Wed Aug 26, 2009 11:45 am

Right on, Ed, it was the RCA 15W circuit that caught my attention thinking EL84, then I looked at the specs and those puppies can crank =:o for a 9 pin.

I will check out the 6CZ5, 6DL5, CV8458, EL95s, also the EH. I'm thinking 9 pin PP but with more power than the EL84.
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Re: 6973

Postby Ty_Bower » Wed Aug 26, 2009 2:01 pm

msmpe wrote:I'm thinking 9 pin PP but with more power than the EL84.


If power is your goal, I guess it goes EL84 < 6973 < 7189 < 7189A.

Would it be considered cheating if you go MagNoval? They've got nine pins, right? ;) All sorts of high power options there... 7868? How about a 6KG6/EL509 or Russian 6p45s?
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Postby TerrySmith » Wed Aug 26, 2009 2:45 pm

The EL84 and 7189 are power pentodes. The 6973 & 6CZ5 are beam power tubes, they look similar but a whole different animal. there's also a 6CM6 that is pinout compatible to a 6CZ5 but lower ratings, it's basically a 9-pin 6V6. All are great sounding tubes!

Don't forget the 6GK6, 10GK6, 16GK6 and 29GK6 family which are EL84's with different pinouts and the three latter with different filament voltages.
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Postby EWBrown » Thu Aug 27, 2009 10:08 am

Then there is the 6GM5 which is essentially a 7868 in a "fat bottle" 9 pin miniature. These aren't very common, and as far as I know, there are no modern production equivalents.

I've been told, though I've never actually tried it, that the 6GT5 (and 12GT5 & 17GT5) is a rough equivalent to 7868, same pinout, just somewhat different ratings, especially the G2 voltage rating. Supposedly they will work as a drop-in substitute in a "pinch". The usual caveats, etc apply for trying this experiment YMMV, etc... However they do make decent triode strapped pseudo-triodes, as dpo most similar TV sweep tubes. As mentioned elsewhere, these horizontal sweep tubes are "insanely" linear. [:)

I'm currently ginning up, at least on paper, an SE amp using 12AX7 or 12SL7 mu-stage (modified SRPP), driving a 42KN6 dual BPT (parallel plates) in triode-strapped mode. Should be good for at least 6W out in SE pT mode. An oddball tube with lots of interesting possibilities. One opf the NNETG guys swears by these tubes, in either SE or in PP modes.

I chose 42KN6s rather than 6KN6s because they're less cost, and I have a perfect filament trannie for these, two 40VAC CT 1A secondaries , and two 115VAC primaries. With 120 in, it should be good for 42VAC out. A flea market foundling for a buck,... I'll be running the 42KN6s at 75-80 mA, B+ 370VDC, and fixed bias (-80 to -110 V grid bias). Plate load 3 to 4K into 8 ohms. The filament demand is 18.9 watts, the 6KN6 gobbles up 3 amps, and the 42KN6 sips just 450 mA per tube.

A PA774, without a heavy load on the filament windings, should handle the PSU duties rather nicely. However, I'll probably use iron with more "heft" just to play it safe.

6KN6s still get a somewhat "premium" price because these have been used in various RF "linear" amplifiers for ham and CB use. The 42KN6s are moatly ignored...

The critical factor here is to use the dual unit (paralleled BPTs), and not the newer, more readily available single plate units. There is a major sonic difference...


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Postby jon_010101 » Thu Aug 27, 2009 8:55 pm

Just a caution on 6CZ5s, while they are about as close to a 6973 as you can get, they do need a slightly different grid circuit for stability. I'd suggest going small on the grid leak resistor (~100k) and adding grid and screen stoppers just to be safe, if the amp is fixed bias.
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