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

[J M Fahey]

Trying to get plate V down (so amp is safer for..) attenuation.

Wonder how you intend to do that .

Specially because 10V relative to 440V is *nothing*.

[Sea Chief]

Hi Mick- sorry Im not with you at all/ have no idea what your referring to (attenuation, the high plate V, power scaling?).

I think I need to refresh the thread; a few avenues have occurred & my arse is down one, my elbow another, and my head floating s'where between!

Im going to concentrate on 2 things. Trying to get plate V down (so amp is safer for..) attenuation.

Thanks SC

[Mick Bailey]

You can temporarily replace a cap from the component side by clipping the existing cap close to the body and soldering onto the existing leads. When you're happy with the result you can do a permanent replacement next time the board is out. You have to work quickly so as not to melt the original joint, otherwise the clipped lead can fall out.

Interestingly, the VHT 12/20 has power scaling built in and it works very well until oscillation kills the MOSFET due to the absence of a grid stopper. Easily fixed with a 200R resistor.

[Sea Chief]

Ok Chuck- done that then/ winging its way from US (one you linked to in fact). Spkr in the DOM is actaully 16ohm.. but main 2 amps 5F1, DR.

I''ll get the DR out & re-meaure across a pair of green 6.3 VAC heater for a check, & re-measure plate V.. last time this rose by 10v or so to 440v for some reason from checking before.

Thanks SC

[Chuck H]

For the 8 ohm unit you need a 25 ohm rheostat. For the amps you own you need at least a 25W rheostat but a higher wattage rating is fine. So, for your purposes, the RJS25R would be the choice.

[Sea Chief]

Juan's glowing write up on VVR/power scaling aside, I think even HE would agree that for an amp like a 5F1 a simple built in attenuator is an easy and fun way to go. And yes... It's a DIY attenuator I use.

Chuck forgive me: Ive just recalled it was you who outlined for me with a circuit diagram, the DIY attenuator.

I cant for the life of me remember where/ which thread its on tho. found it last ev.

In meantime could you just remind me which in your opinion the better one to buy: Ohmite RJS50R (50 ohm, 50w).. or Ohmite RJS25R (25 Ohm, 25w). Ive got both sourced ready to snap up right now.

[Sea Chief]

I think thats a good idea Chuck. As its not complicated by all accounts, could you run me through your components.. maybe I could follow your plan if thats ok? would your 5F1 one be useable on a DR too or do they have to be similar wattagey like a 8w rheostat thing for a 5w 5f1, and a 25w type for a 20w DR? (hope to use with the DOM).

[Chuck H]

Juan's glowing write up on VVR/power scaling aside, I think even HE would agree that for an amp like a 5F1 a simple built in attenuator is an easy and fun way to go. And yes... It's a DIY attenuator I use.

[Sea Chief]

Chuck- are you using a DIY attenuator? trying my 5F1 maxed (for 2 mins sat a'noon!) the strat got just as much OD as the SG.. so maybe if I built one, using the 5F1 as a guninea pig for the DR: Ive got the extra treb on tap in case that subsided slightly. Strat sounds -much- better than SG in the 5F1 fwiw, SG's nr unuseable with this.

[Chuck H]

I'll have to admit that I'm a dinosaur. I still use attenuators. Somehow I've never warmed up to power scaling. I just let the amp do what it does, simulate the load and let some of that get to the speaker as needed. Not a bad way to go at all IMHE. I've never built a power scaling amp. Maybe I'd convert if I did. Somehow I just can't imagine a Marshall that typically has 420Vp and all the other amp voltages following suit with current sag, etc. sounding the same if you tank the plate and screen volts and twiddle the bias in "close enough" Just saying. An amp sounds like an amp when you use it like an amp. Whatever technically "works" not withstanding. But I'm also a proponent of doing whatever sounds good. In that light there's plenty about power scaling I don't know. One thing is for sure. It's definitely easier on the tubes than an attenuator.

[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.

[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.

[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.

[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.

[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.