Search found 2338 matches

by pdf64
Tue Feb 22, 2022 3:37 pm
Forum: Speakers and Cabinets
Topic: Parallel vs. Series Wiring When Mixing SPKR Power Ratings
Replies: 5
Views: 516

Re: Parallel vs. Series Wiring When Mixing SPKR Power Ratings

How it plays out all depends on the details. eg Fender type PTs tend to be rather less saggy than Marshall type, so the HT can be somewhat stiffer, and the ratio of overdriven to clean output power somewhat greater. So even with only 60W clean, the overdriven power may be near 100W. That’s how it wo...
by pdf64
Tue Feb 22, 2022 11:23 am
Forum: Speakers and Cabinets
Topic: Parallel vs. Series Wiring When Mixing SPKR Power Ratings
Replies: 5
Views: 516

Re: Parallel vs. Series Wiring When Mixing SPKR Power Ratings

I suggest to build the amp and measure its actual overdriven power output before committing to speakers. On the face of it, if you overdrive the amp heavily, the 40W speaker will fail eventually. I tend towards series wiring, though Super Reverbs don’t seem to be compromised by their parallel wired ...
by pdf64
Sun Feb 20, 2022 11:15 am
Forum: Fender Discussion
Topic: Fender Pro Junior IV
Replies: 6
Views: 529

Re: Fender Pro Junior IV

Well, the Blues Junior IV seems to have moved to cathode bias, so maybe the Pro Junior has too?
No schematics for either seem to have found their way into the public domain.
by pdf64
Thu Feb 17, 2022 10:36 pm
Forum: Technical Discussion
Topic: Morgan MV45
Replies: 8
Views: 695

Re: Morgan MV45

Bear in mind that traditional HT voltage levels result in the power amp not overdriving until >60W, maybe nearly 100W at full overdrive. Which is ridiculous, seismic loudness.
If a bit of power amp overdrive is desired at a slightly more useful level, a HT down at 375V seems a good thing to me.
by pdf64
Wed Feb 16, 2022 12:43 pm
Forum: Technical Discussion
Topic: Fitting a 100 ohm Humdinder pot to 15w amplifier
Replies: 3
Views: 258

Re: Fitting a 100 ohm Humdinder pot to 15w amplifier

eg as per Gibson GA20 https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga20_12ay7_preamp.pdf Whichever way you go, the balancing node (eg CT) is just a reference, 0 current flows, so I don’t see benefit in routing close to the heater feeds, eg including it in the twisted pair. There’s pro...
by pdf64
Tue Feb 15, 2022 3:28 pm
Forum: Technical Discussion
Topic: Anyone connect suppressor grids to bias?
Replies: 25
Views: 1204

Re: Anyone connect suppressor grids to bias?

I've connected the suppressor grid to GND in cathode biased Amps before, which is more or less the same idea. Make g3 negative relative to cathode. … As I see it, in class AB, won’t the shift in cathode voltage with signal level also cause a shift in g3 voltage, thereby exacerbating cathode bias ‘s...
by pdf64
Tue Feb 15, 2022 3:23 pm
Forum: Technical Discussion
Topic: Anyone connect suppressor grids to bias?
Replies: 25
Views: 1204

Re: Anyone connect suppressor grids to bias?

respond to both: you can see how the top kink is increased, angle too, alowing a little bit more curve to be extracted in PP loadline setted to pass through the kink. so i never seen this for EL34 but why for EL34 or any other pentode would be different effect? can be traced by hand. But what is th...
by pdf64
Tue Feb 15, 2022 10:33 am
Forum: Technical Discussion
Topic: 70's fender bassman 100 head recap?
Replies: 34
Views: 1289

Re: 70's fender bassman 100 head recap?

As I recall, back in the 70s and 80s, high voltage ecaps might typically have a tolerance to value spec as wide as +100 to -50%. So a 80uF cap from then may measure higher than a 100uF +/-20%. The only real effect on performance in circuit is probably in regard of the time it takes for the bias supp...
by pdf64
Mon Feb 14, 2022 2:48 pm
Forum: Technical Discussion
Topic: 70's fender bassman 100 head recap?
Replies: 34
Views: 1289

Re: 70's fender bassman 100 head recap?

Dunno, that’s an engineering query in which the details of particular individual circumstances determines how things play out in various likely scenarios. On the other hand, 550V working / 600V surge F&T KONEL22 axial caps are available http://www.askjanfirst.com/eindex.htm?/hello.htm The caps i...
by pdf64
Mon Feb 14, 2022 12:03 pm
Forum: Fender Discussion
Topic: 5F4 Tweed Super Mod Build--Shorting with Power Tubes
Replies: 21
Views: 4243

Re: 5F4 Tweed Super Mod Build--Shorting with Power Tubes

I found a document that records original Fender transformer model numbers and output impedances. See here: http://www.bustedgear.com/res_Fender_output_transformers.htm I was unsure about the Fender 45216 OT impedance rating as most current reproductions (like mine) have multi-tap secondaries. It ap...
by pdf64
Mon Feb 14, 2022 11:25 am
Forum: Technical Discussion
Topic: Anyone connect suppressor grids to bias?
Replies: 25
Views: 1204

Re: Anyone connect suppressor grids to bias?

g3 should be connected to +5 to +25V ref to cathode, to increase available power. info you can find in about every better pentode datasheet. per example 2E22 where they provide curves for positive g3 Might you be making an apples to oranges comparison? That may be the case for a valve type intended...
by pdf64
Mon Feb 14, 2022 12:20 am
Forum: Fender Discussion
Topic: noisy reverb in ab763 super reverb
Replies: 15
Views: 925

Re: noisy reverb in ab763 super reverb

Has V4’s cathode bypass cap been replaced?
by pdf64
Sun Feb 13, 2022 11:17 pm
Forum: Fender Discussion
Topic: noisy reverb in ab763 super reverb
Replies: 15
Views: 925

Re: noisy reverb in ab763 super reverb

galtjunk wrote: Sun Feb 13, 2022 11:08 pm I replaced the 470 and 1k5 on each 6l6 socket.
I replaced the 100k on v4 pin 1.
So that was all you did, eg nothing else changed?

How about if the reverb is set to minimum / 1 / full CCW; can the dry signal still be heard?
by pdf64
Sun Feb 13, 2022 3:45 pm
Forum: Technical Discussion
Topic: Triode gain stage switching scheme
Replies: 6
Views: 390

Re: Triode gain stage switching scheme

That looks fine, though I don’t understand why the 2M grid leak doesn’t connect to the 0V common rail in the first scheme?
And why SW1 isn’t wired as a bypass? I thought the idea was to engage or bypass the gain stage.
by pdf64
Sun Feb 13, 2022 10:06 am
Forum: Fender Discussion
Topic: 5e5 pro power transformer
Replies: 6
Views: 437

Re: 5e5 pro power transformer

Maybe meant an earlier tweed Bassman, eg 5B6 https://el34world.com/charts/Schematics ... _schem.pdf