DR: OT @ 2 Ohms/ 10" spkr Q.

[Sea Chief]

Gents- (Q1) Ampage guff say Dlx Reverb (AB763) attenuation of sorts can be done by changing OT to a multiple-tap type, using the 2 Ohm wire. Any thoughts? BF/SF Deluxe Reverb | fenderguru.com

Also (Q 2) were any orig blackface DR's with a single 10" spkr? I refer again to Mr. JMarr here: he waxes lyrical about one possible reason his DR sounds so good in a fender DR promo clip "I think its the 10 inch speaker...". (not "..speakerS"): I know they were 2x10 versions but a single 10"?

Combining the 2 Qs you see, I wondering if a combination of things might: attenuate more naturally than a minimass box-affair. Also the nature of a single 10"? what would this sound (in general terms) compared to a 12"

Thanks SC.

[Richard]

A 12" speaker will have more bass than a 10". 12" Speakers are generally more efficient (probably due to more bass) than a 10". I'm not sure about your impedance question; I believe that amps are most efficient at he stated impedance.

[Sea Chief]

Ah ok.. good then I can kill 2 birds with one stone if I replace my Oxford 12T-6 (tho it does sound good/ a vintage one) with a P10Q if I can afford, or more likely a C10R. Both similarly ~inneficient I believe. I also struggle with bass: even a strat via my DR I cant turn bass above 3.5 or it sounds like a cello (& an SG I cant go past bass 2).

I wonder if anyone else has tried a single 10" with a DR? Is it known? I guess JM must be talking 2x10 maybe.

[J M Fahey]

In a nutshell: if you want to attenuate use an attenuator (or wire a variable voltage MosFet in the supply) which:
1) has way more range
2) can be dialed off when needed.

while going to a smaller/weaker/less efficient speaker can vary at most a couple dB ... not enough in the real world and to boot, way less versatile.

[Sea Chief]

Ok JMF understood. I think the switch to a 10" will only address the OTT bass then, which is a good plan all the same.

Never heard if a "variable voltage MosFet " as attenuator.. will my head explode if you were to (briefly) explain?

[J M Fahey]

Never heard if a "variable voltage MosFet " as attenuator.. will my head explode if you were to (briefly) explain?

You mean like this?
https://www.youtube.com/watch?v=GSbigjiKLoU

Oh, please don't ,it's not difficult, and has been used for a few years now, it's what London Power (Canada) calls "Power Scaling", a very clever idea.

In my book, much better than any "attenuator"

Since (any) amplifier output depends on supply rail voltage (as Enzo said, "the power amp is just that kludge between power supply and speaker" ... or something very close) , London Power suggested wiring a variable (pot adjustable) voltage regulator between the power supply and the power amp.
Power Scaling Q&A

You can easily dial down from full voltage, say, +450V to as low as 60V , with power going down as much as you wish.

Of course, it's not only that , they found that if you *only* dial main voltage down many amps sound weird, so in more advanced versions they also dial down bias voltage, PI voltage and preamp output , but those are enhancements, the main idea is that knocking down voltage you knock down power.

If you wish, they sell a full add on kit if you want it already solved in a box, there's also some circuit versions on the Net but you'll have to build them from scratch.

I like the idea very much because the power tubes still drive the speakers direct (through the OT of course) and clip the same, only at reduced power, while conventional attenuators mess things up by definition.

It basically involves adding a power MosFet, with proper heatsinking (it dissipates a lot of power) plus an associated drive board and of course, the regulation pot.

In my book, all tube amps should already includea Factory mounted one, go figure, it is that versatile.
You can dial monsters down to bedroom level (1 W or so).

Best is that on conventional attenuators, power tubes run full blast all the time, while here they have an easier life.

[Dave H]

I also struggle with bass: even a strat via my DR I cant turn bass above 3.5 or it sounds like a cello (& an SG I cant go past bass 2).

I wonder if anyone else has tried a single 10" with a DR? Is it known? I guess JM must be talking 2x10 maybe.

To reduce bass I'd try changing a capacitor before replacing a speaker. Try reducing the value of the coupling cap to the PI grid from 1n to 500p (or lower) and/or reduce the value of the first stage cathode bypass cap from 25u to something like 1u.

[Sea Chief]

Hi JMF. Yes just like the alien, my brain is squeezing out me ears.

But I do understand the basics of what you said above re voltage.

But the "elephant in the room" Q is.. if this is a good attenuation method.. A) why have I read nothing about such a mehtod before, anywhere, and B) why aren't there such devices available to buy?? My alien brain says 'because its not an ideal way to use a PT at all'.

[Sea Chief]

To reduce bass I'd try changing a capacitor before replacing a speaker. Try reducing the value of the coupling cap to the PI grid from 1n to 500p (or lower) and/or reduce the value of the first stage cathode bypass cap from 25u to something like 1u.

I just can't do getting under my RI board: the whole pot pcb needs decoupling/ extracting, then all main pcb wiring undone, bias pot off, 20 pcb mount pillars to undo.. its would take me a whole a'noon to do one cap replacement, without being certain of results. I cant face it.

[Dave H]

But the "elephant in the room" Q is.. if this is a good attenuation method.. A) why have I read nothing about such a mehtod before, anywhere, and B) why aren't there such devices available to buy?? My alien brain says 'because its not an ideal way to use a PT at all'.

Where have you been hiding Chief? Power Scaling aka VVR has been all over the internet for years. In the UK you can get a VVR kit for a cathode biased amp from Barry at AmpMaker VVR Link. A fixed biased amp would need a dual pot to reduce the bias voltage.

[Sea Chief]

Where have you been hiding Chief? Power Scaling aka VVR has been all over the internet for years. In the UK you can get a VVR kit for a cathode biased amp from Barry at AmpMaker VVR Link. A fixed biased amp would need a dual pot to reduce the bias voltage.

Well Ive had amps for 33yrs, asked Qs on attenuation on here and read pages of replies on the subject within a few different threads, & this is the 1st time Ive ever heard of or read anything about 'power scaling'.

Searching 'deluxe reverb power scaling' on google doesnt seem to yield much if any info at all.

Most curious.

[Sea Chief]

Thanks for the link btw.

I guess there has to be -HUGE- caveats to this seemingly simple & innexpensive addition.. or Id have heard of it mentioned 1st off with any talk of attenuation. Why its not even been mentioned, or any eg's on internet, further adds utter mystery to the amp-gtr thing for me.

[J M Fahey]

Well Ive had amps for 33yrs, asked Qs on attenuation on here and read pages of replies on the subject within a few different threads, & this is the 1st time Ive ever heard of or read anything about 'power scaling'.

Searching 'deluxe reverb power scaling' on google doesnt seem to yield much if any info at all.

Most curious.

Maybe your Internet supplier is so slow that he's still feeding you 33 y.o. info?

FWIW my *Argentine* (6000 miles away) google.com.ar yields these results , please click it:
https://www.google.com.ar/webhp?hl=e...+power+scaling

About 4,360 results (0.39 seconds)

including (in a comment on Joe Bonamassa, none the less):

Seymour Duncan Convertible
Seymour made them in the ’80s and it was the first amp to feature power scaling. It could go from 100 watts to one watt. It had different modules, like cards, that would go into the amp and they had tubes in them with different gain stages and preamps. Mine is set up with low gain and it sounds like a cross between a Deluxe Reverb and an early Mesa/Boogie. It’s pretty fun. I talked to Seymour about why they stopped making them and it was just way ahead of its time. They were expensive to make and it almost bankrupted the company, plus they had problems with the cards breaking. You can find them for under $500.

As of power scaling kits:
https://www.google.com.ar/webhp?hl=e...er+scaling+kit

maybe the prioblem is that a conventional attenuator is something you buy, plug and play, literally, while the Power Scaling / VVR must be installed by a Tech , because it's a mod to the amp itself.

Yet, as I said before, *all* tube amps should already have one, factory installed.

[loudthud]

The Seymour Duncan Convertable amps did not use power scaling in the normal sense. The Power knob controlled a pair of current sources that forced the phase inverter to clip. It works remarkably well but I've never heard of anyone else doing it that way. Not even DIY.

[Sea Chief]

I'll have a word with a seriously good amp-builder over here & see what he says re power scaling. It sounds like a sink cleaner.