1624 as DHT triode outputs

[andyjevans]

I have a bunch of 1624 I haven't used, and when considering a 2a3 PP amp I wondered about 1624 in triode instead. Information I have so far is:

- 2.5v filaments at 2A. about 2K Rp in triode, mu about 8-10 (??)
- Operating points are like 1619 or 6V6, not 807 as often suggested.
- Max plate dissipation looks like 15 to 16W, not more.
- Can't find triode curves, so presumably 6V6 in triode is closest?
- Steve Bench reports good results with starved filament
- Can be used as low voltage driver (HT about 200v)
- Some users report microphonics, and also loose plate top caps
- Not sure what value grid leak to use - maybe lower?
- Sound reported as warm and smooth but that's anecdotal
- Probably needs 8K A-A OPT in PP. Maybe 6.6K?

Has anyone any experience of this in triode, and any other information, curves, operating points, OPT values, applications etc?

Andy

[andyjevans]

Here are 6V6 triode curves:

[andyjevans]

I looked at a 1624 closely and the insides look identical to a 807. It's hard to believe it isn't a directly heated version of a 807. The datasheet says 25W dissipation which is the same as the 807. On the other hand the datasheet says "see 1619 curves", and that has a dissipation of 15W. Bit confusing eh!

andy

[pieter t]

Also look at Gary Pimm's Tabor design.
1624 PP.
Gary brought this amp to the Triode Festival in Germany years ago.
I remembered it to sound fresh and open, not "warm" in traditional valve terms.
It is not trioded though.
Need some 1624's? I have some 160 NOS RCA's in the attic.

[andyjevans]

Hello Pieter!

I'm only really interested in triodes, but I take your point about the Tabor. I have 25 tubes myself. Enough not to worry about output tubes for some time!!

Have you tried it in triode, and what did you find? It's also a useful driver I imagine since it has decent gain of around 10. It was originally used in 200W transmitters to drive 813s.

Andy

[pieter t]

Hi Andy,
I never found the time to try them.

[Miles Prower]

Frank's has data sheets for this type.

It doesn't look like the 1624 would do well as a pseudotriode, as it seems to have been designed mainly for Class *2 operation, and doesn't pull very much current with Vgk= 0V. The spec sheet also implies Class *2 operation in requiring that the grid drivers have a Zo= 500R or less.

Easily managed with MOSFET source follower grid drivers. You should get ~70W of audio from a PP pair. Probably best to use 'em that way.

The 1624 is the glass version of the 1619 -- a metal tube. Higher Pd (metal tubes get very hot) and same shape and size as an 807, but definitely not a "DH 807", as the characteristics are quite different.

[DavesNotHere]

yea you'll need to come up with a good voltage doubler for 300V and 600V supply, G2 get 300V bias G1 at -25 out put trannie 100W @ 6.6K, drive with 90Vp-p signal.

[316a]

As a triode 1624 has Ra 2.5k mu 10 so it's like a beefed-up 6V6 . Good for a watt or so SE with 8k output transformer . Two in parallel would be more interesting and could use a 3.5k-4k output transformer but very inefficient , a single 2A3 would do better . Ultra linear probably a better application for this valve .

316A

[andyjevans]

Hi 316a

Do you have any triode curves for the 1624? Is it worth thinking about in class A, either as a driver or output? It's hard to predict this without seeing any triode curves.

andy