6973EH tubes for little Valco amps

[ken]

I just finished putting a pair of matched 6973EH power tubes in a small Valco guitar amplifier.

I was expecting them to work, after all tubes the same number designation are the same tubes... right?

Wrong.

The 'factory original' 6973's used a single 270 ohm 10 watt bias resistor for both tubes, but the new 6973EH tubes redplated in a couple of minutes using the original resistor.

I experimented with resistor values, and found that the 6973EH's sounded best with a 470 ohm 10 watt bias resistor.

Adding a 25uf 100volt bypass capacitor actually made the amp sound dirtier for some reason, so I went with the unbypassed resistor.

just sayin'...

ken

[EFK]

They really don't seem to be the same as the old RCA 6973. I do through a lot of Valcos and while the EH tubes are useful for replacement without having to rewire the sockets, they definitely do not sound very similar to me. As I understand it, the RCA 6973 was a very high-quality audio tube and you can certainly hear it when you can manage to find old stock tubes at a reasonable price.

[Jazz P Bass]

I prefer to rewire (and label) the sockets for a 6BQ5/EL84 tube.
The new EH tubes sound like ass.
And NOS, or even used, 6973 prices are stupid.

[ken]

I know what you mean, I have a Sansui tube home stereo in my office from the '60s that just got retubed with NOS - ouch!

The 6973EH's actually didn't sound so bad in a 15 watt amp with a 10" speaker, but I do think they would sound bad in a bigger amp.
I think the 6973's sold nowadays only have the pinout of a 'real' one, and I wonder what these tubes really are. I think they are some weirdo Russian
servo amp tube or something that got relabeled. However, they 'is what they is'. Maybe somebody at Sovtek got a deal on millions of these, and when they are finally gone we can get something closer to a 'real deal' tube.

ken

[monsteranus]

I have a Valco now I need a pair of 6973's for. Is it a nightmare to rewire for using a pair of 6BQ5/EL84 instead?

[Enzo]

No harder than building anything else. You are wiring up sockets.

The 6973 is a cool tube, it has a lot more capability than the EL84.

[Jazz P Bass]

I ran into this 6973 tube awhile back.
A gibson I think.
The new EH tubes suck & the used/ NOS tubes are going for 30 bucks a pop.
I rewired it for 6BQ5's.
It sounded great.

[nashvillebill]

I hate to hear that about the EH 6973's. I've got an old General Electric home stereo which uses the 6973's that I haven't fired up since I bought it--it's awaiting new caps one day before I turn it on. I hope the original tubes that are in there are still good (maybe I ought to run 'em through the tube tester first).

[soundmasterg]

If you have an amp that uses 6973's and you don't want to use them and you don't like the sound of EL84/6BQ5, you could try using the 6CM6. They're a nice sounding tube that is kind of like a 6V6 in a 9 pin bottle with slightly lower specs. They're cheap cost-wise and sound quite nice.....with a sound closer to the 6973. Of course the socket would have to be rewired appropriately for them too.

Greg

[monsteranus]

One of the tubes had one pin stay in the socket when I removed it. All the pins were bent funny so someone really magled it removing it before. The other tube checks good. Do these have to be matched pairs?

[EFK]

You can also use 6CZ5 if you jumper both pins 1 on each tube socket together, and make sure that your screen feed is running to one of the pin#1. Magnatone and Univox/Lafayette used the 6973 and 6CZ5 interchangeably in the same circuits, and no Valco circuit runs them at the voltages that Magnatone was running. But, YOU MUST have both pins 1 jumpered together and a screen feed on one of those pins (most Valcos do).

I am almost convinced that 6973 and 6CZ5 are basically the same tube (other than the screen feed), but in the handbook, one set of specs are listed as design maximum (6973) and one set are listed as design center (6CZ5), leading one to think the 6973 is a more robust tube.

[Tom Phillips]

This is an old thread but I just had the opportunity to take the attached photo of an RCA 6973 next to a 6973EH. Since the sound difference between these exact two models were discussed above I thought it would be interesting for readers of this thread to see the external physical differences between the two versions of the tube. It is obvious that the 6973EH is not a clone of the original 6973.
Cheers,
Tom