No volt listed on schem

[C Moore]

What do you guys do, or is there anything you can do, when a schematic does not list expected voltage values.?
I have just put this circuit http://www.el34world.com/charts/Schemat ... eg_M12.pdf
into an available chassis. But there are no voltages listed. So what to do.?
Maybe look for another amp that uses the same tubes....maybe a Fender.?
Thanks

[d95err]

The power transformer voltage is acually shown: 700V CT 90mA (i.e. 350-0-350V).

A quick look at the schematic (2x6V6, cathode bias, 5y3) indicates that the voltages are probably roughly the same as in a Fender "Tweed" Deluxe.

EDIT: Hmm... perhaps somewhat higher than a Tweed Deluxe, but in that vicinity.

[C Moore]

Yeah, I get that part.
The confusion comes from the info that I did not put in print. What I should have asked is...I am not familiar with these 6SL7 pre tubes. There is not any voltage listed for them on the schematics, so I am wondering what the typical cat and plate voltages should be for these tubes. Anybody know.?
I have looked at some old Fender schems, but from what I saw, they did not show any preamp voltages on their schematics either. Any idea what kind of numbers I should be seeing on the cats and plates of that first gain stage, PI, and then the Trem Circuit.
Thanks Again

[Phil_S]

There are many things you can do to estimate the voltage. You know the source voltage from the PT, and everything from there is affected by current draw and resistance. Ohm's law is clearly your friend, V=i*R. Learning to use it can be more challenging than it may seem at first blush and I think that is what you are up against.

For a particular tube, I'd start by getting the data sheets: http://tubedata.itchurch.org/index.html

Here's a hint. The 6SL7 is very similar to the noval 5751, which is not too far off from a 12AX7. Study the data sheets and you'll come to see this.

A very handy reference tool appears in the back of the RCA Manual, attached. I found it very dense at first. If you work with it for a while, it becomes useful. There are some tables that suggest how to bias the tube. One of the charts covers the 6SL7.

[C Moore]

OK.
I will take a look and see what I can do.
Thanks

[surfsup]

Funny but I just did this math in another thread:
https://tubeamparchive.com/viewtopic.ph ... 425#154425

3*6SL7 - http://www.triodeel.com/6sl7_p1.gif
1 watt max plate dissipation/300V = 3mA * 3 tubes = 10mA
2*6V6 = 14w/~350? = 40mA *2 = 80mA
screens draw current as well
Screen to grid ratio is 9 if I have that right:
http://lib.store.yahoo.net/lib/thetubes ... -6V6-S.pdf
80/9 = 8.8mA

total amp draw = 80mA + 10mA + 9mA = 99mA

At bottom right, the PT = 700V @ 0.09A (I am thinking this is a tad undersized but should still work because the 6V6s will not be maxxed out ever)

350 * 1.3 = 455V at the secondaries
@ 90mA sag is about 48V
455-48 =~ 408V we'll call it 405VDC

C = 405VDC

B = C - Vdrop of 1kR
V = I * R
I = 99-80 = 19mA
V drop = 19mA*1k = 19v

So B should be 405-19

B = ~385V

A only feeds two 6SL7s so I = 6mA

Vdrop = 0.006 * 22k = 132

A = 385-132 = 253V

I think....

[Phil_S]

The PT should be fine. Remember, in a PP amp, one power tube is "off" almost 50% of the time. We calculate the load as if both tubes are "on" 100% of the time. There is some trade off, as well, for efficiency. No amp is 100% efficient -- far from it, and for that we need to compensate for what gets wasted as heat. Sorry, I'm the wrong guy to opine on an efficiency factor for an amp, so this is only half an answer.