WTF question about electrolytic capacitors

[newguitarsmell]

Hi fellas and Happy 4th

I am now starting a ProLuxe build. The schematic calls for 3 40uf electrolytic caps (c10-12) - the PT is from David Allen

A couple things - the Boothill kit sent me two 47uf caps, and one 22uf cap. Why? Is there some kind of replacement I can use without having to order three 40uf caps or a can?
I have the two 47uf/500V caps and then a 33uf/450V cap - will that suffice?

Also, please note a bias adjustment modification which calls for a  50uf 150V cap (C13) - I didn't get that either...

I am using these transformers so I can use 6L6 tubes instead of 6V6. This is a very straight-forward build, and I have built a 5e3 before and am familiar with it... I like the idea of the souped up version - but am confused about the caps sent me.

Can ya throw me some free advice?  THANKS!!

TP40D
Upgrade power transformer for Deluxe/Deluxe Reverb™ amps. 320V-0-320V at 180ma, 5V at 3A and 6.3V at 4.5A. Supports the use of 6L6 AND EL34 power tubes (power tube sockets must be rewired for use with EL34 power tubes). Center tapped heater winding, 50V bias tap, copper flux bands and internal hum shield brought out to a lead for grounding (ensures the quietest amp possible). 2-1/4" by 2-13/16" mounting centers. Unit is approximately 3/4" taller than a stock PT and weighs 6.7 lbs. Great for high powered 5E3 projects, too.[/size][/size]

The PT is also Allen TO35MT
A high quality replacement output transformer for Vibrolux™, Pro™, Bandmaster™, Vibroverb™ and Tremolux™ amps and "vibroclone style" projects. Custom wound in the USA by Heyboer on a paper tube with paper layered and specially interleaved windings with a 4K ohm primary and both 4 and 8 ohm secondary taps for one or two speaker set ups. As used in the Accomplice, Brown Sugar and Encore amplifiers. Special low insertion loss lamination steel for increased output. Black oxide finish with 12" Unistrand pretinned leads for fast installation. 3-9/16" mounting centers. 2.4 lbs. A very sweet sounding transformer for 2x6L6 amps.

Schematic is attached

[PRR]

The 47-47-22 may be deployed like this without any real change.

However combined with the bias cap being missing, I think you should ask the kit supplier "WTF?"

[newguitarsmell]

Can I bypass the bias section?

[SILVERGUN]

Can I bypass the bias section?

The output tubes need to be biased so the only way you could "bypass the bias section" would be to provide cathode bias.


On the schematic that 50uf 150v cap is not a "modification" it is a necessity.

Do you want to reword your question?

[tubeswell]

Note that going to cathode biasing for the output tubes requires:


1) a cathode resistor (for each tube, or a shared resistor for both tubes). This will deliver more output power if the cathode resistor is bypassed (which requires a 22uF to 100uF bypass cap rated  to take the cathode voltage, and which would probably a similar spec to your missing bias supply cap).
2) that the output tube grid leak resistors be grounded
3) usually will require lowering the screen voltage and/or bumping up the load resistance (if you’re biasing the tubes close to Pmax at idle)


Also, all other things being equal, cathode biasing doesn’t get as much output power as fixed biasing because there is less plate-to-cathode voltage (and therefore less gain). Also, cathode biasing is ‘auto-biasing’, so the harder you drive the amp, the lower the plate-to-cathode voltage gets. Moreover, if you idle the tubes at Pmax in cathode bias mode, it will pull the B+ Voltage down more, further reducing your output power.

[newguitarsmell]

I am going to leave the bias pot in. I found a 50uf cap that will work - and I will order one - and that should be that.
I haven't heard back from the kit guy yet - we'll see what he says.

THANKS FOR ALL THE HELP! Just wait for the pics with the ultra neat wiring job..

[DummyLoad]

who's chassis are you using? just curious. do you have the option to consider the use of the J&J 40/20/20/20? the first section is 40uF that would be for the plates; parallel the second 20uF and third 20uF sections together for the second 40uF; use the fourth 20uF section for the preamps...

respectfully,


--pete

[pdf64]

If a real tube rectifier may be used (ie not the WZ34 Weber copper cap shown) then the hot switching standby arrangement is best avoided.
http://www.valvewizard.co.uk/standby.html

[newguitarsmell]

Thanks for the info.
I will not use a standby switch - and I'm sticking to the bias pot for now.
The chassis is one I got from BootHill. It seems to be the usual 5e3 chassis.

Regarding the bias pot - I heard back - evidently the 40uf cap was too big so it was cut in half to give the tubes more power...

[sluckey]

Regarding the bias pot - I heard back - evidently the 40uf cap was too big so it was cut in half to give the tubes more power...

Say what!!! You either didn't understand what they said or they don't know what they're talking about.

[DummyLoad]

your 6L6GC output stage will be pulling near double the current of stock 6V6 loaded 5e3 - you WANT double the capacitance of a stock 5e3.

respectfully,



--pete 

[d95err]

In general, filter cap values are not very critical. They often have a tolerance of +-20% or so. 40 or 47 should make no difference. In the third stage 22 vs 40 probably isn’t that much of a difference.

[pdf64]

Back in the day, for HT type ecaps, their value's tolerance to nominal was typically +100%-50%, +/-20% would have been mil grade spec.

[newguitarsmell]

OK - here's what he said about the bias cap

"The Weber bias supply design was not good as it did not allow the power tubes to operate at their optimum potential.

Reducing the resistance in the bias supply fixes that issue. Let's the tubes run at 80 percent or so."

He recommended a 22uf/200V cap. That is what I installed so far. What do you think?

As for the bias questions - yeah - I asked that question in a kind of dumb way (what a surprise) - I know I would need to bias the tubes with a cathode resistor instead.

Learning stuff here, guys!