12DW7, 7247, ECC832 -- A Cool Tube!

[stevesamps]

Agree with the great things this tube can do

I just put one in one of my two stage preamps before reading this thread honest!
and viola,
nice and clean but it still had enough gas to drive the PI..
and power tubes, I was also curious which section
was which... I did not even check but it would be very cool
to have one of each to try..

[jrfrond]

Experimentation is a cool thing, a GOOD thing, and we all do it and have done it ad nauseum. However, there are good, solid reasons for designing new builds around common tube types, and I will leave it at that, 'cause y'all know the punchline.

[lookah]

hi. Is it safe to gig my silverface princeton reverb with a 12AU7 in V4 if I don't care about the vibrato being disabled? I eventually intend on getting a ECC823 "reversed" 12DW7 so the 12AU7 is temporary but i don't want to damage the amp if it's "expecting to see" the 12ax7 for the vibrato circuit. I've personally noticed a wonderful tightening of the bass as well as increased clarity when experimenting with a 12AU7 in V4.

[Rhodesplyr]

I see that JJ uses their short-plate version of the 12AX7 triode for this tube. I haven't been that crazy about this AX7 type in most applications, but their long-plate ECC803S is quite nice. I haven't tried them in guitar amps, but they will hold their own against Telefunkens in Hi-Fi circuits and work very nicely in Hammond Organ preamps. I know several cork-sniffing audiophiles who also like them. Perhaps their plate structure makes them microphonic in combo amps, but they might work in a head.

As John Frondelli says, if you can use 12AX7s and 12AU7s, it gives you many more choices. For example, most replacement circuit boards for Dynaco ST-35 amps that used DW7s rearrange the socket connections to use AX7s and AU7s.

I'm glad there's a DW7 in production if I need one for a repair, but I don't think I'd start wiring amps to use them.

[dchang0]

Well, if enough people start using a less-common tube type, then it may become common. So threads such as these, where experimentation with less-common tubes is shared publicly, are a very good thing.

I am very pleased that because of audiophile/hi-fi support for the 6BM8, "cheapo" Electro Harmonix tubes are still currently in manufacture. While I prefer the NOS and vintage tubes, it's nice having that current-production backup tube out there.

Hmm, maybe I should build a one-tube reverb based on the 12DW7....

[Guitarist]

Mark at NOS sells reversed 832/dw7s sometimes: JJ/TESLA ECC832/12DW7 GOLD PINS (12AX7 Sub.) on eBay.ca (item 390296381213 end time 09-May-11 15:24:52 EDT)

Maybe New Sensor would offer some?

[Alexander]

CE Distribution also shows ECC823's in their catalog- their consumer side is Antique Electtronic Supply- maybe email them for availability. I've used over 100 of these DW7's & only had a couple fail & that was from running the 'AU' side too hard. Another vote for designing with an unusual but hi-quality, good-sounding tube!

https://secure.cedist.com/

Antique Electronic Supply

Clearly CE Distribution is the main distributor for JJ/Tesla in the USA- the prices are far better than New Sensor, but if you want 24-hr burn-in for power tubes, New Sensor is still the better way to go! CE Dist just does a quick match-- I've watched cathode current settle over 12 hour periods- IMHO you're nuts to waste money on a 'quick match' like that! Their tech I spoke with said they had no plans for extended burn-inds like New Sensor has. From CE Dist website:

How do you match your power tubes?
We match power tubes based on plate current and transconductance and consider them matched if they are within 2%. We charge an additional $.75 per tube to match them.


Cheers,
Alexander

[km6xz]

Do any of the sellers/rebranders who put a rating on tubes for TC give specs on test conditions? I suspect that the matching is not very reliable when considering the wider DR of a tube in service. I have a batch of tubes I just got for some repairs that all spec th same TC but when putting them on the curve tracer, they differ a lot when sweeping out to higher (but operationally reasonable)anode voltages.

[Alexander]

Most 'matched' tubes are matched at a non-standard plate voltage, may or may not include an actual burn-in, and are merely pairs or quads of just same static cathode currents at given plate volts at an arbitrary but typical grid voltage. I think Eurotubes and New Sensor at least disclose their test conditions...don't use any other suppliers at this point so I offer no opinion.

When I've worked on my own prototype amps with new but un-matched tubes, I have observed quite large drifts of currents over 6-10 hour stretches so I just see no real value in any sort of quick-match scheme, except that at least the tube got hit with 250Vdc to 400Vdc for an 'infant mortality' test... your tubes may not match after a while but they won't be DOA. Small comfort!

[km6xz]

The tubes I tested on the curve tracer this week were New Sensor. They did match at some specific point but not close to normal operating points.
When I had my shop we used to do a lot of old SVTs and we developed a few routines to make tubes last in them. Besides burning in on a test rack where 20 6550s at a time could be cooked, we found that putting in one push-pull pair at a time, and adjusting the load, and watching for even minor variations with current immediately after muting the drive signal, which mechanically stressing the tube, was a great way to come up with a full set that would last 1.5 or more years of roading. Burning in made a big difference in reliability in decades long past, as a way of culling out the lesser tubes, but not many re-branders will care or remove the suspect tubes from inventory. A lot of tubes, which did not test well, were crushed and glass reused when RCA and others were at their peak.
I never had problems with new tubes 40 years ago, they just worked and stayed working for years. But of course no one was running tubes at twice their design ratings either like now.
One of the problems with new tube brands is that few have the technical know how or equipment to really determine what their tubes are doing. I've been to several of the main plants making bulk tubes that are labeled 100 different brands and there is not much real QC or testing of an analytical nature. This summer going back to China and while there I've been invited for a tour of the largest tube company in China, already visited those here in Russia.
The companies doing high power RF and Heating tubes generally have more on the ball since there is still research going on and they have to guarantee specs for minimum full power CCS service, usually 5,000 hours. That is a different world than hi-fi and guitar amp worlds, they actually have to back up what they claim in specs.

[Guitarist]

Anyone tried one of these in a distorting Marshal-style circuit with more proper bias values for the au7 side?

Also, are there any other similar 2in1 tubes like this? A 12at7 and a 12ay7 would be sweet.

[Jazz P Bass]

Please note that these 12DW7 tubes are inherently microphonic.
I would think that fact right there would keep them out of a Marshall, hi gain type amp.

[jmaf]

Please note that these 12DW7 tubes are inherently microphonic.

You mean inherently microphonic like all other tubes?

[Jazz P Bass]

Older Ampeg amps used these tubes.
You run your hand over the tube & they hum.
Tap them & you can really hear them rattle.
And these are NOS tubes!

[Zer09]

Please note that these 12DW7 tubes are inherently microphonic.
I would think that fact right there would keep them out of a Marshall, hi gain type amp.

Are you referring to the new manufacture? I've used NOS 12DW7's and some other substitutions to tame the gain in a Fender Prosonic head that I had. It helps make the gain controls on that amp much more effective. Unfortunately I could never get used to the dark sound from that amp. Never had any trouble with microphonics. I believe they were Tung-Sols.