36KD6 tubes - is there a preferred brand?

[Carl Van Camp]

Hello-

Not sure this group is active any more?  But I thought I would check in.  I am the new owner of a pair of 2SW-1 and want to get new tubes.  Is there a preference for certain brands?  Or brands to avoid?

I'm under the impression that NOS is my only option as nobody makes these anymore.  And there is no substitute for 36KD6 - nothing I could find online anyway.  Do I have that right?

Thank you,

Carl

Chicago

[av]

On the whole you're right. Difficult to find these tubes nowaday. There is a slight variation with a different tube, but that requires a modified socket as well. If you can the find KD36 at NOS - get them.

Happy music listening.

AV.

[she...@shaw.ca]

Hi Carl;  Congratulations on having one of the best speaker systems around.  (and one of the least known)  The only sub for the tube would be 40KD6 which is usually marked with 36KD6 on the same tube.  Bill  St.  Albert Canada.  ps. It would be nice to see more activity here.

[she...@shaw.ca]

On Tuesday, 7 January 2020 10:30:07 UTC-7, Carl Van Camp wrote:

[she...@shaw.ca]

Sorry for the multiple post.  Bill

On Tuesday, 7 January 2020 10:30:07 UTC-7, Carl Van Camp wrote:

[av]

https://www.walmart.com/ip/5-Vintage-RCA-36KD6-40KD6-Compactron-Beam-Power-Tube-Radio-TV-Valve-BangyBang-Tubes/292636583

AV

[John Elwell]

Hi, I've had good results from Sylvania NOS 36KD6 tubes. But I also mixed and matched with good results. My main concern is the possibility of a panel blowing with no one around to repair it. I have a spare, which has sat in my closet for maybe 15+ years and never been used. The good news is the speakers (2SW2's) still sound great after all these years!

John

New York City

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[av]

Great to hear. My panels in my 2 pairs of Model 3s are 30 years old and still work well. That's how Harold Beveridge built them - to last. And they do.

Rick is still doing repairs, has the original mylar stretcher and aluminium mylar. The problem is to get the right tension on the mylar and that can be checked either with a flopover meter which he has, or with a resonance check (a simple jig, laptop software, mic, etc.). He also has the right replacement spacers between mylar-stator if needed, so he can do a full rebuild.

AV.

[Carl Van Camp]

Thank you all, your input is much appreciated.

While we're on the subject of tubes, how about lifespan, can I get a sense of expected replacement rate?  Do they need to be replaced often or are they famous for lasting a long time?

And what about tube matching?  Is it critical or not?

Thanks again, I never imagined I would own a pair of these and I'm pretty psyched to get them running.

-Carl

[av]

Tube matching should be pretty critical as the push-pull on the mylar should be as symmetric as possible (unlike "usual" ESL where it's less important). On the Bev it is important that the membrane travels equal distance in each direction when the same capacitance is formed/varied equally on both sides on either half of the sinus.

Life span?  I would guess around 10-15 years (much depends how much you play them, how many times you turn them on/off). It may be a good idea to buy spares since who knows where tubes will be in the future...  A bit of an investment but worthwhile I think. Also handy if a tube goes pair shaped suddenly.

I should add that I played myself with the original, experimental amp hand build and hand wired by Harold Beveridge (no printed circuits) in 2006. They were built in 1972 as a concept proof. It still worked perfectly with the original tubes and traffo as I connected it to a 2SW speaker! Some tube amp.

If the speakers haven't worked for a long long time, once you replace the tube, it might be a good idea to turn them on slowly via a variac in slow (25V, 35V, 50V, 75V, 90V, 115V, 10mins each), incremental steps. Check the traffo still ok. As you increase voltage, listen for any possible buzzing from the speaker(s). A variac on ebay should cost c.$100-150. Always good to have at home if you don't own one already.

I am guessing you haven't heard the speakers play yet. If you never heard a Beveridge play and you like/appreciate pure sound, you are in for a treat - some say shock.

AV.