The alternative of trying to get a good set of four NOS Mullards is too expensive to contemplate. I could put 6L6GCs or 5881s in but he will loose both power and tone, to say nothing of cosmetic appeal.
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StoSoStu |
KT66 heater current |
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Posts: 663 (10/23/09 00:33) South of the Border..way South! |
Is anyone aware of a current manufactured KT66 that only draws 900 mA of heater current, like the original Mullards? I have some QUAD amps in that need new
KT66s but all the current manufactured ones I look at draw 1.3 - 1.6 A of heater current and the owner is worried that the extra current draw will burn up his
PT. The ones I have looked at are Gold Lion, Shuguang, and Saratov which all draw too much heater current. I couldn't find the heater current data for
JJs, and the owner isn't keen on the Sovtek and TungSol RIs with the metal base ring.
The alternative of trying to get a good set of four NOS Mullards is too expensive to contemplate. I could put 6L6GCs or 5881s in but he will loose both power and tone, to say nothing of cosmetic appeal.
Bob
The road goes on forever and the party never ends |
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SG123 |
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Posts: 8429 (10/23/09 17:30) |
Bob,
I thought for a while this was a trick question since I've never seen a real Mullard KT66 - and never figured there was a KT66 version with a heater current that low. I did find a Philips/Mullard "code" of OS for the KT66, however. I have a copy of a review that appeared on the Tube Store website (might still be there) that seems to imply the "TungSol" KT66 draws the same current as a 6L6GC, but it's been proven they're not even a real KT66. They also have the metal band that's internally connected to Pin 1. Wish I could help..
So many
frequencies, so little time...
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StoSoStu |
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Posts: 664 (10/23/09 21:55) South of the Border..way South! |
Yep, the original Mullards only drew 900mA, so 1.8 amps for the pair, whereas the current stuff draws 1.3 to 1.6 amps, say 3 amps for the two (almost double),
and with an original PT from the 60's I just don't want to be the one to burn out his heater windings.
Bob
The road goes on forever and the party never ends |
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SG123 |
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Posts: 8432 (10/24/09 07:10) |
I fully understand your and the customer's concern.
So many
frequencies, so little time...
Last Edited By: SG123
10/24/09 07:45.
Edited 1 times.
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jbmojo |
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Posts: 453 (10/24/09 08:32) |
Bob over at Eurotubes said the heater current is the same as for 6L6GC's.
Ninty-nine percent of failures come from people who have the habit of making excuses.
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SG123 |
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Posts: 8437 (10/25/09 06:29) |
Aside from the GZ34, I think Brit tube designers, in general, had a preference for high heater current.
EL37 is a 6L6GC equivalent. Heater current - 1.4 amps. I rest my case.
So many
frequencies, so little time...
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StoSoStu |
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Posts: 667 (10/25/09 18:09) South of the Border..way South! |
I was hoping that PBG might jump in on this, he seems to have all the good info on these valves.
Bob
The road goes on forever and the party never ends |
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Psycho Bass Guy |
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Posts: 342 (10/26/09 07:31) |
Aside from a 7581, the "super 6L6," that is almost as rare and pricey, as a Mullard KT66, I don't know, but it does list 900mA as its draw. You might find some oddball RF tubes with plate caps, like the TT21 to the KT88. Is adding a heater tranny out of the question? It's probably the cheapest option.
"I'm the fly in the ointment, the monkey in the wrench, the pain in your ass."
Psycho >^}
Last Edited By: Psycho Bass Guy
10/26/09 07:36.
Edited 1 times.
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StoSoStu |
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Posts: 670 (10/26/09 17:52) South of the Border..way South! |
There's not much room on these QUAD amps to add a tranny. I think the only option at the moment is to go with a standard 6L6GC, they only draw 900mA heater
current. Unfortunately, they don't sound as good, have lower output and don't have, "that look" but at least they won't burn up the PT.
I read on the web that the amp was originally intended to supply power to the tuner unit, which has two or three valves, 12AX7 or similar I believe. If that is the case, and since these units are not connected to a tuner, it may be that the heater windings would handle the extra required for modern KT66s, but until I can confirm all this I'm not prepared to take a chance.
Bob
The road goes on forever and the party never ends |
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SG123 |
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Posts: 8447 (10/26/09 19:27) |
You could always check to see if the filament voltage sags - but that would assume that you'd already bought and installed a set of the new
high-current-drawing valves.
So many
frequencies, so little time...
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Old Tele man |
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Posts: 1479 (11/09/09 19:27) Techus Maximus |
...instead of using the "good-stuff" oxide coated cathodes, it seems that some of the imported tubes have resorted to "cheap" oxides and
HIGHER filament currents as a trade-off.
...many people are reporting unexplained "higher" than original NOS filament currents, and likewise increased filament "sag," so check for this possibilty on UNDER achieving amplifiers with new imported tubes.
"...Renovatio, non Exauguratio..."
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