Rectifier Tubes

[CraigGa]

I'm still planning on building a Benson Monarch clone in the near future so decided to see what was left in my tube stash and I have some of these rectifiers.

20210426_160001.jpg

The CV378's are dated 7103 and the 5R4GY's isn't dated but they are probably from the same era.
The CV378's appear to be equivalent to GZ37 or 53KU

I've also got a bunch of 6939 double triodes, are these any use in audio?

Can anyone enlighten me on these?

Thanks in advance
Craig

[TUBEDUDE]

5R4's are great rectifiers. The 6939 is a twin power pentode usually used in R.F. class C service.

[Phil_S]

https://frank.pocnet.net/sheets/079/6/6939.pdf

[CraigGa]

So there's not much call for a 6939 in a guitar amp then. Shame because I have a box full of them.

[Stevem]

I have never seen any logic ( no less long term economy! ) to building a amp that you will hopefully love and want to live a long life buy using tube types that you have ( in your stash ) and that you may not be able to get good ones of in the future if even get at all?!

[Phil_S]

So there's not much call for a 6939 in a guitar amp then. Shame because I have a box full of them.

If you are the adventurous type, build it and see if you like it. If you do, then you have a box full of spares. If you don't, you can change to EL84's (noval socket) or drill it out to take an octal socket. Just leave enough room to drill it out for the octal. Have some fun along the way. IMO, not much to lose if you don't like it. Any effort is a worthwhile learning experience.

[CraigGa]

I wasn't intending to cheap out on the build, I was thinking that a NOS 1971 government spec rectifier made by Mullard would be a better tube than anything available today if it was compatible which it doesn't appear to be.

My initial search for the 6939 described them as a Double Tetrode which I misread as Double Triode and doesn't mention that they are primarily for RF use.
I guess the 6939's are destined for the trash if they are of no use in audio, I'll hang on to the rectifiers incase they're useful to anyone.

Craig

[Phil_S]

Don't trash them. eBay value is $3-$5 each. Sell them. Someone wants them.

[CraigGa]

Hmmm, I could by my new tube set with a few of those
The rectifiers are listed for big money but there is a lot of them on there already

[Phil_S]

Check the box for sold items only when you do the search. This will tell you how to price them for a quick sale on eBay. For the 6939's I suggest a BIN price for the whole lot at $4 x the number you have will get them taken off your hands quickly. I didn't look at the rectifiers. It's a win-win. You get some money to buy what you want and someone who wants 6939's will be happy to take them off your hands. After all, 6939's are now made from unobtanium!

[CraigGa]

Thanks Phil, I'll look into it.

[didit]

Those rectifiers are valued by audio types, particularly the CV378. One might sell both and net more than enough to purchase suitable transformer set for the Monarch with perhaps even some leftover cash for tubes and more. You can compare specs with Benson's choice of GZ35 and decide how suitable either would be for your take on his design.

Best .. Ian

[CraigGa]

Thanks Ian,
Actually I've got 3 or 4 of each so It might fund a but more than that

[Phil_S]

Ian got me to look. Sold listings for CV378 start at $55 and go up from there. "Tested" ones (whatever that means) are above $100 and go to over $200. There is a "new" (if you believe it) NEC that sold for $430!

5R4's are all over the place, between about $5 and $100.

I think you've got a small treasure there and it may fund your habit rather nicely!

[thetragichero]

sold a mullard cv378 date code B7G5 (5th week of july 1967/1977 blackburn plant) for almost a hundred bucks on reverb a few months back. i got it buying out someone's tube stash. probably could've made a few bucks more on ebay but i've been burned too many times selling stuff there

i second selling and buying guitar amp tubes