Tremolo

[Mats]

Hi
Did look at a topic here and the schematic for a Silvertone 1449/1457.
The tremolo in that SE amp is connected to the Cathode resistor of the Power tube. That resistor is split in to two.
Thats a new thing to me.
I have seen tremolo-signal connected to,  first triode or pentode, second triode, Grid-leak resistor
before Power tube but not this.
Good thing to learn new things.
Any for or against with this kind of tremolo (Silvertone 1457) ?
/Mats

[tubeswell]

Going by the voltages and values on that silvertone schematic, that 6V6 is idling at 17.6W! (I'd say it'd work better with 470R in series with the 33R as a cathode resistor.)

The reason they have the split resistors is to attenuate the LFO bias wiggle. You could experiment with different values of split cathode load for a bit of fun.

Interesting LFO circuit

[Willabe]

http://www.el34world.com/charts/Schematics/files/silvertone/silvertone_1449.pdf

[Mats]

Thanks for replay and link to schematic.
Yes its a different kind of LFO.
What about using a Cap over the 270 Ohm resistor ?
I think I will try it out.
Would it work in a cathode bias, Power tubes, PP amp also ?
Split the Cathode in two as in the Silvertone 1449.

[PRR]

> tremolo in that SE amp is connected to the Cathode resistor of the Power tube.

No.

Well, yes it is; but that's not how it works.

The trem buffer yanks on the 100K resistor which feeds the plate of the first stage. The wobble-B+ changes the gain of that stage.

(I would not expect much action; this may be more about having "trem" yet avoiding Fender's patent than getting you the very-best trem.)

And the 33 ohm tap? The trem oscillator needs a cathode bias. This will typically need a _big_ bypass cap, an electrolytic. Electos in hot amps are trouble, especially in the bad old days. Note that there are _NO_ electrolytics in here except the one (3-section) cap-can. Taking a couple Volts from the VERY low impedance 6V6 cathode gets the right DC voltage without a trem bypass cap.

[PRR]

> 6V6 is idling at 17.6W!

I get 14.3W.

15V/303 is 0.0495 Amps. Plate-cathode voltage is 305V. Total input is 305*0.0495= 15.1W. Rule-o-thumb for 6V6 is screen takes 5% of current, so plate gets 95%. 15.1W*0.95= 14.3W.

AFAIK, 6V6 has always been good for 14.0W "measured". The 12W rating allows a lot of slop-factor. SilverTone surely did not measure every unit built, but this is a CHEAP student-set and probably had a short warranty with little or no coverage of tubes. The average recipient annoyed his parents and himself from Xmas to New Years, lost interest. If he really had moxie and talent, the first problem with this amp he'd wangle a "real" amp from somewhere.

EDIT: 90 days parts tubes and labor, One Year parts+tubes but you pay labor. That's fairly generous for a burning-edge build. But what's the worst can happen? The amp burns a tube AGAIN, you are right near the Sears Showroom, the tech suggests that maybe a power-player like you should consider a bigger amp, and the Sears salesman is right there ready to demo the Real Amps.

[Mats]

Thanks for replay and the trem-schematic.
So this is how it works.
Follow up here, looked at Gibson GA-40 Les Paul and its tremolo
and how the 6SQ7 act together with the 5979.
Little different, but it is much the same to change the gain of the 5879 ?
Once again big thanks

[tubeswell]

> 6V6 is idling at 17.6W!

I get 14.3W.

Then I misread the plate voltage - I thought it said 370 (not 320). Mind you I was looking at this one http://www.el34world.com/charts/Schematics/files/silvertone/silvertone_1449_1457.pdf

[PRR]

> thought it said 370 (not 320)

See what you mean.

Follow through OT to 6X4 and C9C. I see "330V". It's reasonable to lose 10V in OT primary, impossible to gain 40V. Therefore I think "370V" is a fly-speck or scratch on the old parchment.