ampeg v6b transistor substitutions

[dropanchor812]

Hey there, so I'm fixing up an ampeg v6-b, 240 watt transistor amp.  It's had a bunch of issues, but right now I'm fixed on messing with the power section.  Here's a service manual and schematic:

http://bmamps.com/Schematics/ampeg/Ampeg_V-6B_Service_Manual.pdf
http://elektrotanya.com/ampeg_v-6b.pdf/download.html

So, the proper output transistors are 2n4348, and there are eight of them.  I received this amp with 4 of those transistors substituted with three SK3297 and one 2N3773.  Now, I don't know a whole lot about the specs on these, and from what I can glean from my own research is that both of these might be a tad under spec'd for this amp.  But, maybe I'm reading the datasheets incorrectly and they're actually fine.  I've gone to alltransistors.com and looked for substitutions and from what I can tell I think other RCA output transistors in the same series, but there's another odd transistor, SK3260 that looks like it would be almost a perfect sub.  Here's a link:
http://alltransistors.com/crsearch.php?mat=Si&struct=NPN&pc=120&ucb=140&uce=120&ueb=7&ic=30&tj=200&ft=0.8&cc=&hfe=15&caps=TO3

Then, there are a problem with the driver transistors.  They're weird and there's little to no info on the internet anywhere about them, especially the one that's broken.  There's zero continuity over the two legs of the one labeled STA8236.  It's in a TO-66 package.  I saw on a another post on another forum someone recommended using an MJE15030, which is in a different package.  I could do this, but I'd love to keep the correct package. 

Any recommendations?  Thanks!!!

[Enzo]

Why would those subs be UNDER spec?  They have higher voltage and current ratings.  But you really want all four to be the same type, whatever you use.

SK series transistors are a replacement line, similar to the NTE line of today.  Don't use them, they will be hard to find anyway.

COntinuity?  Are you using diode test?  If so, does reversing your leads make a difference?  One driver is PNP the other NPN.

TO66 transistors are not around in large numbers, though I may have them.  Nothing dishonorable about using other shapes.  Having original is fine, but to me anyway, not worth holding up an amp for months.

[J M Fahey]

That 2N4348 replacement salad should be replaced (all of them for consistency) by superior MJ15022 which are still available at Mouser @$5.50  each, not a bad price.
As of TO66 drivers, sadly you must forge them (unless you get NOS ones from, say Enzo´s stash ... IF he has thm that is):

TO66 package was discontinued LONG ago (think 30 years or more)  and was never very popular to begin with, so .........

Modern TO220 replacements can be :

Q302 NPN driver: MJE15030 , available at Mouser for $1.50

Q303 PNP driver: MJE15031 , again at $1.50

You can mount them with just one screw, bending legs so they match TO66 leg position, and if socketed and socket needs 2 screws for stability, add  the second one but pass it through a nylon nipple or bushing so it does not short to metallic chassis or heatsink, it does only mechanical duty.

This is an excellent but dated design, so some parts are simply not available any more; yet modern ones work perfect, just with a slight tweaking.

Post a couple pictures showing original transistors mounted, heatsinks, etc.

In general rectangular shapes such as plastic TO220, TO218, TO247 can be adapted instead of old oval "fried egg"  metallic ones, although in very few exceptions the old ones fit tightly or at an angle or in custom tight fitting cast heatsinks and corners get in the way.

EDIT:
as of

There's zero continuity over the two legs of the one labeled STA8236.

that´s a confusing statement.
Please use the diode scale which displays the voltge drop when passing a few mA of current and quote the humber, as in: 0 (short) , 700 (or 0.7) (expected diode drop), open (blank display or a plain 1 with no other digit visible) .

[dropanchor812]

Thanks for the comments guys.  Initially, I was just using my Ohm setting on my DMM to make sure the transistors weren't open.  And now, yes, I have done the diode test.  As far as the driver transistors go-  one is giving me a measurement and the other one is not (it's giving the "1" reading), no matter how I connect the probes to the leads.  That's leading me to believe that the driver in question doesn't work-  unless there's a secret I don't know about.  So-  do I need to replace the pair of to-66 drivers with the MJE15030/15031 combo, or can I just sub in one of those components for the transistor that isn't working?   

As far as replacing the power transistors go-  it looks like I will go ahead and replace them all-  but for testing purposes, just to make sure that the whole thing at least sort of works, can I leave these transistors in?

Here's a couple pictures of the transistors and the PSU.  I'm not really addressing the PS board right now, but it may come up later... probably.   To explain all the red wires, I attached insulated bullet connectors so I can remove the board more easily, instead of having to desolder the whole thing if something else goes wrong.  I also need to replace two of the power transistor sockets at some point (but that's only evident from the other side of the heatsink).  The main problem with the  power board was that one of the traces actually burned through the board.  It was only a single length between two components, so it was easy to solder in a solid jumper.  But I'm wondering what made that happen in the first place...  If y'all want a picture of that too then let me know.

I hosted the pictures on imgur and their embed code isn't working for me... hopefully this link will work for you.

http://imgur.com/gallery/xXWRH

[galaxiex]

Here's your pics. 

[dropanchor812]

Here's your pics. 

Thank you! :dbtu:

[phatt]

As far as replacing the power transistors go-  it looks like I will go ahead and replace them all-  but for testing purposes, just to make sure that the whole thing at least sort of works, can I leave these transistors in?

Er,,, how would that help?  They are already dead or dying and will just burn something again. :duh
Replace ALL before you fire it up again other wise you will just go in circles.
I assume you know about using a lightbulb limiter when testing new components?
Phil.

[J M Fahey]

As the old carpenters say: measure twice and cut once
which here might be understood as: work slow, don´t hurry, play it safe, replace all suspect parts , use the bulb limiter, and you will meet success.

Beautifully made old school amplifier, almost choked seeing that big heatsink chock full of transistors.

You will be rewarded with a killer amp, way over specified (with the new parts) , will last ages.

[dropanchor812]

Thanks for the advice everyone, I'll get the new parts and proceed from there.  And yes, I have a light bulb limiter.  I'll give an update once i get the new parts in, thanks!