Can a 6x5 drive PP 6V6 guitar amp

[scstill]

Looking for advice as to whether a 6X5 can support the current draw of a push pull 6v6.

I have this crazy vision to make something unusal with an old Packard 6V car radio and a power transformer that I pulled from a Webster Chicago 2010 reel to reel

The Webster 2010 (schematic below) drives Push Pull 6v6 with the 6x5 and the transformer that I have. But is 210v on the 6V6 plates going to be high enough for the guitar amp?

The tubes for the amp will be (2)6v6 driven by a 6SQ7 PI, driven by a 6SK7 pentode preamp on channel 1 and a 6SQ7 triode Preamp on channel 2. This is the setup in the packard radio, and I think it would be cool with these tubes as a guitar amp. I calculate the Webster 2010 pulls 90ma HV for plates which is about what the guitar amp tube set would draw

0504201130.jpg

[pompeiisneaks]

Just looking at a couple different datasheets, tung sol on both it shows for push pull class ab1 for two tubes at 285 VDC on 6V6 the screen and plate current add up to 105.5mA
that doesn't include a few milliamps for any preamp tubes, like 20 each or so I think? I'd have to double check.

The 6X5 datasheet shows a max current of 210 mA per plate and it shows two so I'd think it can do double that, but don't quote me. (shared cathode but separate anodes, you could just tie those together into the same current path)

So yes, it seems to me that for a 2x6V6 it has more than enough current handling capability.

~Phil

[roberto]

Based on these datasheets:
6V6: https://frank.pocnet.net/sheets/127/6/6V6.pdf
6X5: https://frank.pocnet.net/sheets/127/6/6X5.pdf

6V6 will have 74 mA per pair at idle in AB1 at 285 V and 105,5 mA with g1=0 (page 2).
6X5 has a standard working condition at 70 mA with peak at 210 mA (page 1).
So yes, you can use it.

You will se a drop of 22 V at idle (page 2) and around 30 at peak.
Do not exceed 40 uF as a first filter after the 6X5 (bottom of page 1).

[didit]

Hello -

It'll work fine. Schematic shows 230VDC at the first filter capacitor, which makes sense based on 210VAC secondary. That 6X5 rectifier works. With those voltages and paraphase PI it will have a unique voice that will work, for some definition, as guitar amp. Early '50s and and perhaps (at a guess) about 10 Watts.

Best .. Ian

[scstill]

Thanks for the good insight into the rectifer. I will be moving forward with this design.

As a follow up, what do you think about using the power transformer in the Webster schematic?

It physically fits perfect in the chassis, but I wonder if the HV secondary will be a limitation in the design?
Today I set up a breadboard with the xfmr and 6x5 (have 2 tubes both were identical), got the following measurements

• 120vac in
  6.3v at heaters
  250-0-250 Vac on HV sencondary
  225vdc at 6x5 cathode

Doesn't the 225vdc seem low for 6v6 as PP?
Would I just extrapolate the performance from page 2 of 6V6 datasheet?
with design points at around 7watts and 12,000load resistance (for example)

When I add a 22uf from cathode to gnd I measure 342vdc (K to gnd). Thanks Martin
So now do I need to drop some volts or will in lower just with teh 6V6 load?


BTW - was very odd that the xfmr only has 6 wires.
Dilemma - where are the center taps?
Turns out the CTs are to the case. Interesting design...

[martin manning]

Got a reservoir capacitor connected from the cathodes to ground?

[scstill]

Got a reservoir capacitor connected from the cathodes to ground?

When I added 22uf as you suggest, It measures 342vdc (k to gnd)

So now should I plan to drop some volts? Or will it be lower with the 6V6 load.

[pompeiisneaks]

When all the tubes are in place and conducting it will drop voltage a decent amount. You also mentioned the voltage being too low for 6V6 earlier, that's actually about what they like... 265 I believe.

~Phil

[scstill]

Excellent...

Now for another follow-on question (moving forward whats best to ask here or start a new thread?)....
The original Webster Schematic (from which I am basing the pwr supply) shows a choke after the 6x5 and 1st cap
I have that part but never have built a guitar amp PS with a choke, if it fits in the chassis, should I use it?
What would be the difference between an LC here and RC.
Any tonal impact?

[Phil_S]

I can't comment on total difference. The LC circuit will most definitely have an impact on plate voltage and current available. If you spec'd the PT assuming choke input, use the choke. If you are going to omit the choke, then you may/probably want a different PT.

As an aside, there are some old PTs floating around that have lower than ideal high voltage output that can be "made suitable" for use by using FW choke input. I had one like this that caused me to start a thread that discusses choke input and shows results of my tests with several chokes. You might search for it. It's a few years old.