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Substitute for a 6973 tube: 6EM5?

guitarcapo

Senior Member
Messages
2,326
O.k. here's the amp:


http://elektrotanya.com/PREVIEWS/63463243/23432455/magnatone/magnatone_280a_sch.pdf_1.png

Uses FOUR 6973 power tubes that routinely cost $35+ a tube....$140 for a quad. OUCH.

Well, I can buy THESE NOS USA made for $3 a piece. very close but lower plate voltage rating. TEN for the cost of just one tube!


http://www.nj7p.org/Tube4.php?tube=6EM5

Think they can handle it? How would I bias with no cathode resistors? Should I reduce the plate voltages with a different rectifier tube? Am I dreaming?
 
Last edited:

guitarcapo

Senior Member
Messages
2,326
hmmmm. No responses after 36 views. I guess I'm on my own. I guess I'll plug 4 in and stand back. Lets see if these tubes can handle 375 volts on the plates or if they'll melt.
 

EFK

Member
Messages
1,048
One thing I can tell you, after owning a good number of 6973-based Supro amps, is that NOTHING sounds like a real RCA 6973. Spectacular tube - I think RCA poured most of their hi-fi tube making knowledge into that one. The new EH tubes will work very well in old 6973 amps *but* to my ear they don't sound anything like a real 6973. It's not even an issue of them being "a bit off" or anything subtle; it's quite a dramatic difference. They are dark and somewhat dull without any of the extreme clarity and open chime of a real 6973. If you plan to keep the amp, spend the money for old RCA 6973 tubes and be done with it - you'll probably never have to retube it again and I assure you that your ears will thank you for it.

FWIW, and on the other hand, if you are trying to build (from scratch) a 18-20 watt Marshall type amp and want a darker, very mid-oriented tone, I think the new EH 6973 hold some promise over the more commonly used EL84.
 

LarryN

Member
Messages
955
Re: RCA's. I agree. RCA anything is hard to beat. NOS 6973's are like hen's teeth. Too bad about the EH's. I had an Ultratone amp from Australia with a huge AC step-up transformer thrown into the bottom for US use. It used 6973's. Cool clean-ish tone.
 

AL30

Member
Messages
3,001
I think you can use a 6CZ5 tube but you'll need a small rewire. You should also check the data sheets and compare the two.

AL
 

guitarcapo

Senior Member
Messages
2,326
The problem is basically maximum plate voltage ratings with either the 6CZ5 and 6EM5. The 6973 is a true audio output power tube with higher plate voltage ratings. These others were made more for televison sets or something. I think if I was rearranging pin-outs somehow I'd be better off converting the amp to use EL84 tubes. They can use the same output transformer because the impedances are in the same ballpark and can handle the higher plate voltages.
 

AL30

Member
Messages
3,001
I think it's only one pin (maybe two). It's a simple mod if I recall. The info is out there but I haven't looked in a while. And yes, you'll need to check the voltages.

AL
 

Rumblefish

Member
Messages
2,735
Ask Terry Dobbs at valcoamps.com. He showed me how to wire the sockets to accept 6cz5's in my Airline /1624t style amp. He and I both like the 6cz5 more than the 6973.
Be sure to get tall bottles.They come tall and short.
Tone Quest report raves about 6973's and how superior they are to el84's.
I've often thought it would be cool to try these tubes in an old Matchless or Vox.
 

Jon Silberman

10Q Jerry & Dickey
Silver Supporting Member
Messages
41,957
Does anyone know where to find NOS RCA 6793s? My searches today have come up empty.
 

Leonc

Wild Gear Hearder
Platinum Supporting Member
Messages
18,243
$49 bucks for that adapter does seem pretty stiff!

My good friend Terry Dobbs made the one I used in that video, btw.
 

Leonc

Wild Gear Hearder
Platinum Supporting Member
Messages
18,243
I have used 6EM5s as subs for 6973s and can vouch for them in some amps. It's a question of voltage put out by the amp, as the OP points out. The 6EM5 can't take everything that is 6973 can. But there are plenty of amps in which it's not an issue...and thr 6EM5s sound great!
 




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