Late 90's Peavey Transtube Supreme repair (power transistor questions)...

[Steve Conner]

Well, I thought the Mouser ones looked fine. The markings agree with the marking diagram in the latest ON Semi datasheet

http://www.onsemi.com/pub_link/Collateral/MJ15022-D.PDF

and the font is the same as some genuine older MJ1502x I have here. I'm fairly sure they're genuine because I haven't managed to destroy them yet. Notice that some of them have off-centre printing too.



If you turn them over, and they have the larger blue glass seals, that would be another point in their favour.

[tube power]

I accidentally left the reverb tank unattached when I put this back together.
It's a 4 wire plug that will go in either way.
I use a Carbon Copy for slapback, no reverb, so I don't care as long as leaving it
unplugged does not hurt the amp. (It sounds great.)
But if I sell it I'd like to plug it back in.
Anyone know how to tell which way it goes in?

[nashvillebill]

The 4 wire plugs I've seen on Peaveys had an arrow-shaped end which corresponded to a cutout or something on the chassis.

But if you can't tell by the plug, look at the tank, one connection on the tank is labelled in and one is labled out. Then check the schematic and trace the in and out on the PCB to find the orientation of the plug.

[tube power]

The 4 wire plugs I've seen on Peaveys had an arrow-shaped end which corresponded to a cutout or something on the chassis.

But if you can't tell by the plug, look at the tank, one connection on the tank is labelled in and one is labled out. Then check the schematic and trace the in and out on the PCB to find the orientation of the plug.

Thanks.
What happens if you reverse it?

[nashvillebill]

The input and output on a reverb tank performs different functions; one end drives the springs, the other end picks up the signal from the springs. While you can get a signal out of a reverb tank if the input and output is swapped, it's not the way the unit is intended to operate and it likely wouldn't sound that great.

Here's a reverb tank explanation:

Spring Reverb Tanks Explained

[Enzo]

Oh, just plug it in, if it is backwards, the reverb won;t work. Then you just reverse the plug.


Most PV cables these days end in IDCs, not the individual crimp pins. So the arrow thing is history.

[J M Fahey]

Hi Steve, thanks.
Good to know.
All Motorola , ON, ST, and in fact any "serious" company used to print straight and centered, I guess the sloppiness found everywhere comes from cutthroat competition.
Oh well.
Worse than that, is that in the past you could count on parts standing from 20% to 40% *more* than datasheet specs, if not all at least a sizable 40 to 60% which could be selected to use in critical work; nowadays the *good* ones just cover specs with no room to spare.
I had to tighten my short protection to the point of starting to be heard.

[Steve Conner]

Hi Steve, thanks.
Worse than that, is that in the past you could count on parts standing from 20% to 40% *more* than datasheet specs

Well, in Hartley Peavey's white papers, he quotes Jack Sondermeyer of RCA as saying, "Those transistor datasheets are bullsh*t, and I know, I wrote them."

Hartley Peavey thought he could use the maximum ratings in his transistor datasheets the same as the ones in tube datasheets, but Sondermeyer persuaded him that they were absolute maxima never to be exceeded, or ideally even approached. Persuaded as in, he quit RCA and went to work for Peavey, designing classic solid-state amps like the CS800, with considerably more pairs of output transistors than Hartley's old designs.

I aim to run power transistors at no more than half of their rated dissipation. This gives headroom for instantaneous peak power, and also allows for the fact that the dissipation rating is for an infinite heatsink. I don't design products for the mass market, though, so I have more leeway, I don't need to pare the costs down to the bone.

[Wayne]

Dear Masters,

I've just found that the volume of my Peavey Studio Pro is much smaller after a period of loudly play(volume @ 9 about 15mins). I replace the transistor with MJ15024G & MJ15025G then burn out the 3A fuse.

I Know nothing about electrics and could you please kindly help to shoot my problem?

My appreciation in advance.

B.Rgds.
Wayne

[J M Fahey]

PLEASE don't consider this a rude answer, quite the contrary, but considering

I Know nothing about electrics

(I commend you on your frankness) please first get somebody who has some experience (meaning ideally experience on repairing something related (HiFi, TV, stuff like that) or at least who has successfully built an amp or a couple pedals).
Unfortunately such skills are quite uncommon these days, since most (all?) stuff is exchanged or replaced instead of repaired.
Although you seem to have an original problem, it's probably still unsolved and compounded by the maybe unnecessary transistor swapping.
Sorry.

[thesynthdr]

Just to let you know this info is still helping folks repair this amp and do it in a way that it wont come back fantastic thank you for the info and sharing Sam

[thesynthdr]

thanks for the info a fix that wont come back I like it Sam