Re: wiring FrankenVox AC15 for 6AQ5's and 6BQ5's?
- From: "Phil S." <psymonds_no_spam@xxxxxxxxxxx>
- Date: Fri, 9 Jun 2006 22:58:05 -0400
"Jim" <askme@xxxxxxxxxxxxxxxxx> wrote in message
news:128jo8lq23s3lb6@xxxxxxxxxxxxxxxxxxxxx
Phil S. wrote:
I'm getting near the end of the FrankenVox AC15. The plan is to wire a
pair of 7-pin sockets for 6AQ5's and a pair of 9-pin sockets for 6BQ5's.
The questions::
The 6AQ5's call for a cathode resistor of 250z and the 6BQ5's call for
130z (in this case it will be 125z). In doing the wiring, is this as
simple as wiring one 6AQ5 and one 6BQ5 from each pair in parallel. I
assume this works, as long as only one pair or the other is present in
the sockets. Then, wire the cathode with two 125z resistors, one of which
is on a bypass (on-off) switch?
I'll be using 1.5K grid stoppers and 100z resistors of G2, both tied
directly to the tube pins. These will be present on all four sockets.
Is this a problem? Or is it better to simply pair up one 7 and 9 pin
tsocket and wire strictly in parallel, essentially using the (one set of)
grid stopper and G2 R to do double duty?
Or is it necessary to to something more elaborate to get this right? I
understand that the user needs to know to only have one pair present in
the circuit, and that will only be me. I can always write on the head
with a Sharpie to keep unlikely fools from thinking one could acutally
run this amp with 4 power tubes. There isn't enough B+ or filament
supply for it, not to mention how they might interact. If I like it
better one way or the other, I can look at making it into a Frankenvox
AC30 <grin>.
It is possible that I'll have to supplement the filament supply as it is.
I saw a nice small 6.3v 0.3A tranny in Radio Shack for $3.99. It is PCB
mount, so it will require a bit of ingenuity to make it useful.
Thanks for comments and advice.
Phil
If the existing filament winding is weak anyway, have you thought about a
completely separate filament transformer, so that you can play with a
variac for the rest of the circuit?
Hi Jim,
I know the filament winding (based on the tube compliment of the donor amp)
will support the 6AQ5's, (0.9A/pr) unsure about the 6BQ5's (1.52A/pr). but
the extra 0.6A could easily be within reach. I'm guessing that an old PT
will perform somewhat beyond original application. If not, I can add a
separate FT; these are cheap and available. (BTW, as I write this I see
that the RS tranny isn't good for much except a couple of preamp tubes. My
mistake.)
As for the rest of the ckt, the PT runs about 255-0-255 without load. With
tube rectifier and under load, this should be just below the 310v the Vox
schematic indicates (255 * .85 *1.4 = ~303). IMO, this pretty much eclipses
the variac idea, no? Besides, I don't have one ;~{
Anyhow, it's an interesting idea and thanks for the suggestion.
Phil
.
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