Need help: Marshall 2199 repair

[BigBoy]

I came to this forum sincerely hoping to find the advice needed to fix this amp. I gotta say I'm pretty disappointed, with almost 500 reads and yet no one has taken the time to really help. Oh, well.

[phatt]

I'd fly over and have a better look at it for you,,, but my private Jet has a flat tyre. :lmao:
Phil.

[phatt]

All TO3 bipolar transistors have the same pinout.   

All bipolar TO220, TO218, and TO247 transistors have the same pinout - ECB across the front.

I knew the TO3's where all the same but was not sure about the other tab types.
Arrh darn You Enzo you got me again  :grr,,, I must owe you a point then :tu:
Cheers Phil.

[BigBoy]

I did, however, find a source for the same types Marshall used originally, so I may just get them and try them. Since the amp came to me without the originals, it's kinda hard to know what the true original failure mode was. I reckon I'll keep melting lead till something good happens....

[J M Fahey]

I came to this forum sincerely hoping to find the advice needed to fix this amp. I gotta say I'm pretty disappointed, with almost 500 reads and yet no one has taken the time to really help.

REALLY?
Replies 1, 2, 9, 11, 13, 14, were technically correct and in good faith.
Replies 3, 6, 7, 8, 10, 12, 15, 18 were written by yourself.
Boy, you *do* like writing to yourself ... and throwing tantrums too, alienating those who want(ed) to help you..
Oh well.

[joecool85]

I did, however, find a source for the same types Marshall used originally, so I may just get them and try them. Since the amp came to me without the originals, it's kinda hard to know what the true original failure mode was. I reckon I'll keep melting lead till something good happens....

Looks like this is your best bet (to use the original ones and go from there).  Let us know how it turns out.

[BigBoy]

Mr. Fahey, with all due respect, I differ with your assessment of the posts. The only ones that furthered the endeavor were the suggestions for replacements for the original Darlingtons. I took that advice, and the amp works, but draws too much current. So, something needs to be changed. Neither you, nor anyone else, has offered any suggestions as to what might be done to the circuit in order to reign in the current draw of the new output transistors I installed.


Were you in my place, would you not be frustrated?

[J M Fahey]

Dear big boy.
There *is* people here trying to help you, for free, on their own time, and guessing a lot because they do not have the amp in front of them.
Please show *them* some respect.
And repairing amps goes step by step.
Usually when you repair something, you find something else, but only then, nobody sees the future.
You were suggested to use TIP142/147 which , although plastic, *do* fit in the original sockets.
"Plastic TO3" (rounded top), TO218 and TO247, both rectangular, were designed with such purpose in mind.
Of course, they only use 1 screw and not 2.
TIP142/147 exist in any of those TO3-compatible cases, yet you chose to use TO220 cased ones, which do *not* fit and need all kinds of funky modifications.
By the way, you still owe us

please post a couple pictures of where the original heatsinks were , what you mounted now.

That info is neccessary because you probably have thermal runaway and the bias compensation transistor is not thermally coupled to the heatsinks.
EDIT: not having emitter ballast resistors certainly does *not* help.

[Enzo]

BigBoy, may I point out that just now I checked, and the forum is being read by 8 members and 103 "guests."   That ratio is common.  Do you realize that forums like this are regularly scanned by robot visitors for places like google and yahoo?   When you google a topic and find a post in some forum like this one, it is because of exactly that sort of visitation.  So when you see 500 views on your post, the vast majority of them were not members at all.   SO don;t be thinking it is like a bunch of us sitting here refusing to respond.


it is like asking strangers on the street for directions, you can hardly count the folks riding by on the bus for not responding.

And sometimes members read the post and move on, having nothing worthwhile to add.



I make an effort to help as many people as I can over here, maybe not very many, but I do resent it if someone thinks I or we are obligated to solve all problems.  "You are not helping me enough," is not a very warm message to be sent.  I suspect others feel similarly.  This is not a simple "my amp broke" repair.  You have parts missing, and are now trying to install parts other than those the circuit expects, and when that doesn;t work, you want re-design service from the group.

My good faith help:  If it draws excess current with the different transistors, reduce the bias differential between opposing bases.  TR9 is the bias transistor, so make it turn on harder.  Does the bias adjust RV1 in fact turn the current draw up and down?  And so it is just a matter of range?  Or was TR9 or the resistors around it damaged when whatever esle went on it the past damaged the rest of the amp? Raising R34 should increase conduction of TR9.

[joecool85]

I think there has been a lot of good help here and bigboy is just frustrated because he is having a difficult time getting done what he wants done.  I totally understand, I've been on both sides of the situation even here on this forum.

No worries, it looks like you guys understand each other more than you think  8|