I think I effed up my 4210 plz help

[vinceB]

So here is what happened. The speaker lead shorted red to black, sparks ensue, amp now has no output. The HT fuse is blown tried another and it blew instantly. What have I done?!

 

[RickyLee]

Sounds like it is time to test the output transformer as well as the power valves.

That's is a bummer. How did the speaker cable get shorted together?

 

[vinceB]

it was a loose connection and it slid off and laid across the other lead. Probably when I pulled the power cord out of the back.

 

[FutureProf88]

I would say get her to a tech. You may be looking at a new OT.

That's rough, man... :frown:

 

[vinceB]

Okay I forgot my meter at work but I pulled the tubes out and put a new fuse in and it survived. Put the tubes back and instantly the fuse is blown. I'm going dig out my schematic and look it over because I'm not sure what I'm looking for when I check the transformer.

 

[chuckharmonjr]

Have you tried another set of tubes?

 

[Steve Naples]

^^^^^ Like Chuck said.....

 

[vinceB]

I don't have any spare el34 tubes. It's my first Marshall in many years. (I had a Line 6 with 6L6's) It has the original Sovteks from 1989 I believe. The gentleman I bought it from told me it's had the same tubes since he got it in 1995. Either way they are old and I want to replace them but before I place the order I need to be sure I don't have to also order a transformer.

 

[vinceB]

Fixed that connection on the speaker though. I may solder that SOB on for good. I do not want a repeat of this fiasco.

 

[FutureProf88]

Try new tubes first. Look at it this way: If you buy new tubes and then find out the transformer is blown, you wanted to replace the tubes anyway. You already have the tubes so then you can research your transformer options.

If the tubes fix the problem, great. Then you're set and don't have to worry. Tubes are the lowest cost, lowest headache option here.

 

[Ken]

Shorting your speaker lead should NOT fry your OT, at least not right away (it will on a SS amp though!). You proved it's okay by pulling the tubes and seeing the fuse survive. Tube time!

Ken

 

[HaenC]

Shorting your speaker lead should NOT fry your OT, at least not right away (it will on a SS amp though!). You proved it's okay by pulling the tubes and seeing the fuse survive. Tube time!

Ken

True, OT's are tough guys.

 

[damienbeale]

It hasn't proved the OT is okay at all. It has merely proved that the ot hasn't failed in a dead short or short to ground, which is a very rare occurrence anyway. Marshall OT's are not that tough either.

All that said, you need to try new power tubes before you can go any further with this.

 

[vinceB]

I bought a matched pair of burned in Winged C's and it sounds amazing.

 

[69ChevyP/U]

Whew!!

What speaker do you run in that amp? The g12t-75 in mine is hitting the highway. I'm leaning toward a g12-65..

 

[Ken]

I bought a matched pair of burned in Winged C's and it sounds amazing.

Tubes seemed the likely culprit. I'm glad it turned out that way!

Ken

 

[vinceB]

There is something screwy with the clean channel I discovered today. It's real choppy and very sensitive to pick attack. Like the signal is barely there until I hit the strings hard then the output is inconsistent and harsh sounding. I need to bias the tubes so it's still "down" but I sure would like to figure out the clean channel

 

[BILL B]

Hi Vince
Just finished working on one, sounds like your coupling caps are gone...

 

[vinceB]

That's weak. I was going to buy an new cabinet but I think I'm going to be spending a lot of money getting this old girl into shape. I had a 2205 years ago and I'm trying to find that sound again.

 

[damienbeale]

Hi Vince
Just finished working on one, sounds like your coupling caps are gone...

Pardon? That's a bit rash.

Try cleaning pots and jacks first and carefully checking the solder joints.
It sounds like a bad contact, not bad coupling caps.

Clean tube sockets and retension the pins too.