Yellow Jacket EL-84 Adapters?

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Yellow Jacket EL-84 Adapters?

Postby kevco » Wed Jun 23, 2010 4:55 am

http://www.radiodaze.com/T-YJS-converter.htm
Can these be used in the ST70? I doubt it's something I'd actually ever get around to trying, but I'm curious if they'd work in the Dynaco's circuit.
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Postby burnedfingers » Wed Jun 23, 2010 5:03 am

Looks to me like you would have a lot wrapped up in fancy adapters that would result in a **** poor sound in my opinion. There are a lot of different output tubes that one could use in the 70 however the EL84 isn't one that I would use. If cost is a consideration the 6BG6GA and the adapters is a reasonable choice.
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Postby Geek » Wed Jun 23, 2010 6:03 am

They are made for guitar.

I have no idea how they sound for HiFi, but then I have never heard of anyone use them for such a purpose.

Take your ST-70 to a music shop that retails them and do an experiment? They'd probably be just as interested as you in the result (as it would broaden their market too).

Cheers!
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Postby EWBrown » Wed Jun 23, 2010 9:55 am

Unless the adapters have some sort of voltage or current limiting (apparently they do) , the ST70 plate voltages will probably launch thosee EL84s out of the YJ sockets, like miliature Polaris missiles ;-) But then, I don't se how limited V and I will rsult in clean sound...

Seriously, the B+ in the ST70 is almost 100VDC higher than the EL84s can safely withstand, and the plate curent is about 50% too high, which is a rather deadly combination for these smaller tubes.. (There are ways to run them of much higher B+ voltages, at lower currents, but the ST70 circuitry is not compatible with these unusual approaches)

Probably want to put the fire department number or 911 on your speed-dialer before you try this dangerous experiment in electro-pyrotechnics

In a nutshell: DON'T try this at home, or anywhere else, except perhaps at the Nevada Nuclear Test Site (Area 51, Groom Lake, etc). These yellowjackets will deliver a very nasty sting :'( (666) >:o

/ed B
Last edited by EWBrown on Mon Dec 20, 2010 9:17 pm, edited 2 times in total.
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Postby kevco » Thu Jun 24, 2010 7:36 am

I sent an email over to the manufacturer, and this is his response:

"You can...that said usually in your home stereo you want more head room and Yellow Jackets will lessen that."

Question answered.
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Postby burnedfingers » Thu Jun 24, 2010 4:33 pm

No, question answered incorrectly.

As Mr. Brown has stated the B+ is way too high for those tubes to survive.

You cannot use the Yellow Jacket adapters with the EL84's and expect survival.
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Postby Geek » Thu Jun 24, 2010 4:49 pm

....the B+ is way too high for those tubes to survive.


Yes they can, as long as the screen is held at 250V or less (lotsa circuits on how to do that).

We covered this topic before here:
http://www.diytube.com/phpBB2/viewtopic ... 700v#24213

Cheers!
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Postby jonnyeye » Thu Jun 24, 2010 4:57 pm

My guess from reading that page is that the yellow jackets have:

1. a cap in series with the grid pin, with a grid resistor on the EL84 side,
2. a cathode bias resistor, and
3. zeners to reduce the plate and screen voltages by about 100V

all inside the yellow tube. So you'll be turning your amp from fixed bias to cathode bias, and inserting another cap into your feedback loop (of unknown quality and capacitance). I'd say it's best to skip these for hi-fi.
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Postby burnedfingers » Fri Jun 25, 2010 4:39 am

Quote:
Yes they can, as long as the screen is held at 250V or less (lotsa circuits on how to do that).


I guess I should have said that they aren't just a plug and play insertion. But still why in the hell would you want to use them?
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Postby Ty_Bower » Fri Jun 25, 2010 7:42 am

6bg6ga wrote:But still why in the hell would you want to use them?


They might be handy for a guitar amp in situations where your fifty watt 6L6GC amp has too much power. Maybe you're playing a small venue, or you're just practicing in the garage.
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Postby Geek » Fri Jun 25, 2010 3:04 pm

Ty_Bower wrote:They might be handy for a guitar amp in situations where your fifty watt 6L6GC amp has too much power. Maybe you're playing a small venue, or you're just practicing in the garage.


That's exactly what they were made for.

Cheers!
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Postby kevco » Sat Jun 26, 2010 7:46 am

My understanding from a friend who uses them in EL-34 based guitar combo is that they do in fact tame the power of that amp for practice use, but also allow the amp to be pushed into overdriven distortion without the usual insane volume levels associated with that. Heavy metal tone, lullaby volume.
Last edited by kevco on Sat Jun 26, 2010 10:41 pm, edited 1 time in total.
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Postby Geek » Sat Jun 26, 2010 3:07 pm

I say just try 'em and see if you like them :-)

Cheers!
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Postby kevco » Sat Jun 26, 2010 10:23 pm

Geek wrote:I say just try 'em and see if you like them :-)

Cheers!

I did! I borrowed two pairs of Yellow Jackets from my guitar toting buddy, mounted my NOS Mullard EL-84's in 'em and sat down for a listen....Nice tone, plenty of power for my 99db./meter efficiency speakers. I could still hear the unmistakable tone of the EL-84's as I dragged my family from the burning wreckage of our 250 year old homestead. Very nice. Highly recommended if more than 20 watts stresses your eardrums! Can't wait to try 'em in the MC 275! ....As soon as we rebuild and get the glass out of the cat. :)
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Postby TerrySmith » Sat Jun 26, 2010 11:04 pm

I guess what we need to do now is bust one of these yellow jackets open and see whats inside!
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