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ICBM

Just acquired another old knackered amp for free today - a Peavey 'red stripe' Transtube Studio Pro 112. Which brings up some interesting points:

First, you *can* kill a solid-state Peavey. Somewhat disappointingly, Peavey switched to using integrated power amp chips in these, instead of discrete transistors - if it dies, and then you put a 10A car fuse in the amp, it will fry the bridge rectifier as well and then burn out the speaker, making the amp uneconomical to repair (at least commercially).

Second, it was made in 2000. That makes it *nineteen years old*, or only two years younger than my first amp, an ancient 1964 Centurion, was when I got it in 1985 - which seemed like it came from a different world - and yet to me, this Peavey is a totally modern amp. Time flies...

Third, since I don't like to throw away stuff if it can be fixed even if not really economically, I've replaced the fried components and stuck a spare Celestion Hot 100 in it, and it really sounds very good . So I'm going to keep it, at least until something even better comes along!

Winny_Pooh

Flog it to a rehearsal studio

ICBM

Winny_Pooh said:

Flog it to a rehearsal studio

I did think about that, but I’m not convinced it’s totally bombproof enough - the discrete-transistor ones are, to date I’ve never seen a single one from this series die - but these integrated power modules do seem to fail more often even though they’re supposed to have inbuilt overload protection.

The speaker I had is 16-ohm rather than 8 though, so in theory that will make it more reliable... and I need a better workshop/small gig amp anyway.

DJH83004

Never had one on the bench IC, are they typical TDA type output chips or some kind of Peavey custom design? if the former then yes could be a risk especially in a rehearsal room environment, they can decide to blow up if the wind changes direction - (as you know only too well   

ICBM

DJH83004 said:

Never had one on the bench IC, are they typical TDA type output chips or some kind of Peavey custom design? if the former then yes could be a risk especially in a rehearsal room environment, they can decide to blow up if the wind changes direction - (as you know only too well   

It’s a LM3886T. Peavey must have got it nearly right though - this is still the first of these amps I’ve ever seen dead. The heatsink is enormous by normal standards for this size of amp. I’m hoping that running it at 16 ohms will be enough to put it on the right side of the line!

ecc83

What are the supply voltages IC? The data sheet for that chip suggests you will get about 25-30W into 16R for a +&- 35V supply.

The speaker destruction mode is I assume because the chip fails latched to one supply rail or the other? Have you considered  a 2,200 uF cap in the speaker circuit?  Or,  Maplin used to sell a speaker protection relay kit, had a "plop" supressing switch on delay as well. Their "150W" MOSFET module was good as well but that was dropped long before their demise. Velleman might still have the protection kit? Will have a shufty...

Dave.

ICBM

ecc83 said:

The speaker destruction mode is I assume because the chip fails latched to one supply rail or the other? Have you considered  a 2,200 uF cap in the speaker circuit?  Or,  Maplin used to sell a speaker protection relay kit, had a "plop" supressing switch on delay as well. Their "150W" MOSFET module was good as well but that was dropped long before their demise. Velleman might still have the protection kit? Will have a shufty...

Far too much of a faff . It’s the usual everything-on-one-PCB arrangement - power supply, power amp, speaker connections, the lot. (Other than the preamp.)

I don’t want to hack the board... given that this is the only dead one I’ve ever seen, and that when I got it all the gain and volume controls were full up - not conclusive, but a possible clue as to how it died in the first place! - I doubt there’s much risk of re-failure, especially running at 16 ohms.

35V supply rails, yes. Peavey claim 65W into 8 ohms which may be a bit optimistic! Anything around 30W into 16 would be plenty for what I need it for. If I can be bothered I might measure it...

DJH83004

It certainly sounds like it is not being pushed too hard, especially with a 16 ohm speaker, +/- 35v supply rails and a big heatsink. Its such a shame they went away from the earlier discrete transistor versions, they were virtually bomb proof!

ICBM

DJH83004 said:

It certainly sounds like it is not being pushed too hard, especially with a 16 ohm speaker, +/- 35v supply rails and a big heatsink. Its such a shame they went away from the earlier discrete transistor versions, they were virtually bomb proof!

They were, and the bigger models still use them - from the Bandit upwards - this is the largest model with a power IC.

I have to say it sounds absolutely great too... it may be the Hot 100 - I actually quite like them, they're a little like a high-powered Greenback G12M-25 to me - but it can nail the sound of an old Marshall Super Lead I was working on this morning, albeit at much lower volume! Really amazingly so for an amp that's worth at best £100.

brooom

You had 1964 Danelectro Centurion? What did you think of it, I always wondered what that circuit would sound like.

ecc83

Fair enough IC but you could just cable tie the cap' to the speaker basket?

Going to see what a "Hot 100" looks like. I think I fitted one in place of a Peavey spider a few year ago.

No, I fitted a G12K-100 with the MASSIVE magnet. It was a stereo 135W pch combo and the R/H speaker had a stuck cone (blown VC) The Celestion was just as loud as the left speaker  even though it was 16 Ohms.

That was a nothing job my son dragged home from some impecunious muso at the Labour club. "Sure! My dad'll fix that for you!"

Dave.

ICBM

brooom said:

You had 1964 Danelectro Centurion? What did you think of it, I always wondered what that circuit would sound like.

No, a Centurion - obscure British amp company - 'Hi-Fi-Five', which is an oversized 2x8" combo that's neither hi-fi in any way or even really five watts .

ecc83 said:

Fair enough IC but you could just cable tie the cap' to the speaker basket?

Considering that I've put the right fuse in the amp, even another IC failure is unlikely to do the speaker any harm.

ecc83 said:

Going to see what a "Hot 100" looks like.

Roughly M-magnet modern Celestion a bit like a much better Seventy/80. I'm not convinced it's a true 100W speaker - I've seen a couple blown in applications which shouldn't stress a traditional 100W Celestion - but that doesn't matter here since it won't be taking even half that.

brooom

ahhh, got it... that's a different amp altogether!