Tube Amps / Music Electronics
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|6/3/1997 2:33 PM|
||How hot should 6V6's run?|
The 6V6's in my 1969 Deluxe reverb get REAL hot! Like they will burn you if you touch them - WAY hotter than the 6L6's in my other amps. Is this normal? One of the (sovtek) tubes just blew and I replaced it with some old GE tubes from a 1946 Hammond organ amp. These old tubes sound great - very soft and actually distorting earlier than I would like, but in a good way. Out of four tubes I found only one that did not glow cherry red on the plate. In biasing the amp I found the glow came at about 40mA and up. I finally ended up at about 32mA to get the plate voltage down to 425V and the bias voltage to about -36V as shown on the schematic (re: biasing advice in Weber). I am going to replace these with new tubes in a day or so, and I don't have any idea how old or worn the Hammond's 6V6's are, but should I worry?
I did remove two 1200pf parasitic suppression caps from the plates, but reconnecting them did not change the red glow...
What kind of 6V6's does everyone like?
|6/4/1997 12:07 AM|
6V6s are pushed hard in that amp. The best replacements would be a pair of RCA black plates if you can find them. GE, Philips, Sylvainia are also good. The Sovtek ones will work ok if you sort through a bunch to find a good pair. Find a good tech who has a supply of them.
The results you have with old tubes depends of course on how hard they were used. They may just sound kind of flat or the may just give up under the high voltages in the Deluxe.
An interesting fact concerning the Hammonds is that some of them installed in institutions (or even some homes) were under a maintanence contract and had the tubes replaced every year. Some of those tubes only had a few hours on them and are still good.
|6/16/1997 12:55 AM|
Hey John, Run your NOS 6V6s at
28-35 ma. Do not use any new prod. 6V6s in a Dlx. rev. They are junk. Don't worry too much about getting plates below 425VDC. Jim Kelly ran them in the 480s. Make sure filters are good. Lift the grid end of the coupling caps on the phase inverter and make sure no DC is leaking to the grids of 6V6s. Such a condition will throw bias way off. I have 100s of NOS 6V6s and all sound good to killer. My favs. are RCAs from the 50s w/silver logo and smokey looking bottle. Good luck. Paul
|6/16/1997 4:46 PM|
Isn't 35ma per 6V6 awfully hot for a Deluxe Reverb? At 400 plate volts, that comes out to a plate dissipation of 14 watts per 6V6, which is right at the rated maximum. This is essentially biasing for class A operation, and I'm not sure the transformers are designed to run at such a high idle current (at that high a voltage) for a long period of time.
I once experimented with running my '68 Deluxe Reverb with 5881's idling at 30ma each, and I got nervous when I realized how hot the power transformer/chassis was getting (yes, I realize I was also taking a chance by running at 900ma extra filament current). I switched to NOS 6EY6 running at around 25ma each. (If you can find them, NOS 6EY6 and 6EZ5 are excellent 6V6 replacements).
|6/16/1997 8:39 PM|
Yes, 35ma does get 6V6s close to class A in a Dlx. Rev. but they are not on for the full cycle as in true class A. A few months back I serviced a Jim Kelly 30/60 w/ blown pt. After research, and a lot of phone calls later I decided ( w/my clients approval) to replace the PT with a Thordarson, designed for a Twin Rev. It put 480 vdc plates and 475 vdc grids at 35ma per tube on the qt. of nos 60s Sylvania 6V6s. In a Dlx Rev. 28-35 ma is a range. I normaly set bias at 30 ma unless the player wants less head room then I'll set it up to 35 ma but no higher. Check out the schem. for the JK 30/60 in the Tube Amp Book 4th. Edition pg. 741. If you think Leo was hard on 6V6s, Jim Kelly brutelized them.
|6/20/1997 8:46 PM|
Just today I found some NOS 6EY6's so I put them
in my '69 Deluxe Reverb. I also put in a GZ34
to offset the additional filament current from
the 6EY6's (the amp came with a 5U4GB).
When I set the idle cathode current to 29mA,
I measured 440 volts on the plates. I also
measured the voltage across the screen resistor (.82 V), which if I calculated correctly
means the screen current is around 1.6 mA.
Again if I did the math right, this is an idle
plate dissipation of about 12 watts. Is this
too hot, or in the ballpark for 6EY6's?
Also, should I have just left the 5U4 in,
even with the additional filament current, just
to keep the plate voltage lower?
|6/22/1997 10:10 PM|
The rectifier heaters and power tube heaters don't realy have anything to do with each other cus' they are on different windings in the PT, 5v and 6.3v respectivly, so the power tubes don't care what the rec. current draw is and vice/versa.I would drop in the 5U4, 5V4 or 5Y3 in this order, to get the voltage down some. Design max. for 6EY6= 250VDC pt. @ 44 idle ma. (RCA Receiving Tube Man. #24) per tube. So you can see you need to get the B+ down a bit. Specs are for class A operation (harder on tubes cus, the're on all the time) and DR is AB (with tubes on a little more than half the time) so you could afford to push them them a bit. I would shoot for 380-425 v on pt. @ 28-35ma with whatever rec. got it there.
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