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make sense to swap a 6AQ5 for a 6V6

7/3/2000 8:17 AM
fopoman make sense to swap a 6AQ5 for a 6V6
Would there be a tonal change for the better if I swapped a 6AQ5 for a 6v6. would I have to modify a fender musicmaster to do so?  
Thanks for the help  
7/3/2000 2:12 PM
Chris Hurley

You would have to modify the musicmaster for a seven pin socket, for starters.  
Secondly, the 6aq5 may not take the voltages which are present in your musicmaster.  
The 6aq5 and 6cm6 are evidently similar to a 6v6 in a different size bottle, so the tonal differences might only be similar to trying a different brand of 6v6.  
I've heard tell of people running 5v6's in 6v6 amps with good luck, although you'd probably want to put a series resistor on the heater connection to get the voltage down for long term use. The 5v6 is a 6v6 intended for 5v filament duty. They are tremendously less expensive than the 6v6 for this reason.
7/3/2000 3:55 PM

I've owned two of these, both the 6AQ5 version. The B+ is only about 305V, so voltage is not going to be a problem. 6AQ5 are fairly abundant in NOS, but not many people bother to match 'em. Great little tube, but it's essentially a 6V6 in a mini 7-pin bottle, so I don't know if there'd be any point in changing between them, unless you're sitting on a bumper crop of 6AQ5s in your attic....  
C ya,  
7/3/2000 3:00 PM

The 6AQ5 version of that amp was only made a couple of years, I wouldn't change it personally but that is up to you. You would have to cut the chassis out to change from a 7 pin to an octal socket. It would probably be a good idea to put new caps in the amp though. It is a very simple design and is easy to work on. Mine is the 6AQ5 version, and I kinda like the way it sounds after a simple tune up. A better speaker will go a long way with this amp. New tubes will probably help too.  
7/3/2000 6:15 PM

No doubt the 6AQ5 was supposed to be electrically equivalent to the traditional 6V6.  
There are still differences in construction, and there can easily be differences in tone even between identical matched tubes if you listen to each one separately in an amp that is made for a single power tube.  
So I would expect you to hear a difference, but no one could predict whether YOU would like it better or not. Just because a 6V6 type was (& still is) a much more common guitar tube, it was not intended to be more suited for this purpose. They were both just common cheap low-power tubes designed to do the same thing but use different sockets. To a degree, since the 6AQ5 does have lower maximum voltage ratings than the original 6V6, and the 6V6GT can in practice handle even higher than that.  
In a circuit that originally had 6AQ5, the 6V6 types would be expected to perform the same. OTOH, with an original 6V6 circuit that happened to use higher than the 275VDC max of the 6AQ5, it might put the 6AQ5 under a little stress if it was tried as a substitute.  
One of the few characteristic curves in the GE Essential Characteristics book of 1973 is for *this* tube. The title of the graph is Average Plate Characteristics for 6AQ5, 5AQ5, 12AQ5, 6AQ5-A, 5V6-GT, 6V6-GT, 12V6-GT, 6V6-GTA. (By then the original metal *bulb* plain 6V6, and *coke-bottle* glass 6V6G were discontinued but belonged here electrically too.) It shows plate & screen current at various grid bias voltages while varying the plate voltage from zero to 400VDC and leaving the screen voltage constant at 250VDC.  
I would use whatever tube type was intended for the sockets originally, changing for newer tubes or different brands is likely to make as much difference as you would get by modifying the amp to have sockets for the alternate component.  
Hope this helps,  
7/11/2000 12:43 AM
John Beard

I've got a Jensen from my '66 Pro Reverb in this amp for now, and it sounds great. What would you consider a "tune-up" for this amp, and would you change the values of any caps etc? I use this amp for recording, cranked it's especially loud but sounds great. Thanks for any info.
7/11/2000 1:22 AM

As far as a "tune up" for this amp, I would replace the filter caps, and check the resistors for drift. I replaced almost everything in mine. The original coupling and tone caps my have been OK, but every resistor in this amp had drifted so I just replaced about everything while I was at it. There really isn't much in it, and of course new tubes. I put a 10" ceramic speaker in mine and I like it better than a 12", it seems a little "brighter" to me.  
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