Ampeg B-15n HELP!!!

[stompjunkie]

I've been working on an old Ampeg B-15n. It came to me all blown up. The cap off of the ground switch was almost completely gone, and it took a few of the leads and resistors around it with it. I've replaced all of the components that were obviously bad, and I tested most others in that area. I installed a much safer 3 prong power cord etc... I'm able to power everything up, and it seems to stay on and is stable....

Is there a good voltage chart out there for these? I know I've gotten reasonable voltages, but I'd like to see what this circuit calls for.

I'm not getting anything out of it though. Not even a little hum. I've checked all of the obvious things I could (bad joints, bad leads, input/output jacks etc...) So, what do I do next? What are the chances it took the OT out when it fried?

Thanks for the help. Being stumped can be very humbling.....and I'm certainly feeling humble....

[Cygnus X1]

You took out the death cap, right?

I had this problem once when I forgot to tie the secondary center tap of the power supply to ground. Everything looked fine, but no ground reference made it dead.

[da Geezer]

If you have another known good OT laying around (any PP unit will do for a quick test) you could "tack" it in & see if you get any sound....

I had a B15n blow the OT several months ago....confirmed it with the method described above. The guy chose to NOT repair it at this time, as the Fliptops replacement (Heyboer) is ~$300 or so.

edit: after looking at fliptops.net, I see the OT is actually $219....I guess the 300 bucks I quoted him must'a been w/labor...

[selloutrr]

measure the resistance Note which leads connect to the B+ line, measure the resistance from the B+ line to each plate of the output tube(s). Measure each side of the push pull. Both sides should measure within a few tenths to a few hundred ohms of resistance. over 1K = burned = Dead. If it's open it is DEAD!! I've had a few like that. Now try each leg to chassis ground if it's not in the high K to probably megohms it's shorted and DEAD!!

It saves you from swapping transformers before you know it's bad.

Best of luck!

[selloutrr]

if it's dead of you need any Ampeg parts try www.fliptops.com they are very knowledgeable and willing to assist.

[tubetek]

If it is one of the models that uses an XLR type speaker connector, be sure to defeat the safety interlock. Two of the pins in the XLR need to be shorted in order for there to be output. I had to deal with this many years ago when I used a B-15N for guitar with a different cabinet.
Tom

[da Geezer]

if it's dead of you need any Ampeg parts try www.fliptops.com they are very knowledgeable and willing to assist.

link didn't work...it's ".net" > http://www.fliptops.net/catalog/index.php

[stompjunkie]

Thanks for all the help guys. I'll have to wait a couple days till I can get back to it. I'll be sure to try all of those tests. Thanks again, and Happy Holidays. I'll be sure to keep you posted on how it works out.

[selloutrr]

sorry about that! .net!

[austinb]

Look for a string of diodes across the output transformer that may be shorted. Most ampegs used them.

[stompjunkie]

Hey guys here's the update...

I've got sound! There was a resistor that was cracked in half. It looked perfect from up top, but I saw a hairline on the side by the bottom... I gave it a chopstick poke and she split in two. I must have missed it in my other chopstick test. I hate how long it can take to find things like that that shouldn't be there.....

On to the bad news.... I've got some serious motorboating. I didn't replace the giant cap can, and I imagine that it's gonna have to go. Thanks to you guys I actually have a source to get one now. I guess I'll have to order one up and swap em out.....

What else could be causing this? It's a very strong motorboat, and it's a fairly low frequency if that helps at all.....

Thanks again guys!

[selloutrr]

Motor Boating is a symptom that The signal from the decoupling capacitors in the B+ lines of the preamp section are going high impedance, and not decoupling properly. replace the B+ decoupler cap in the preamp section first. If the other electrolytic caps are 15yrs or older or show signs or bubbles or corrosion replace them as well. it's capacitor related. best of luck soon you'll have a kicking bass amp!!!

[tubetek]

Hey Stomp-
Is that a non-pcb model with all octals? 6SL7s etc? IF so, what a classic!!
I've overhauled one and left the cap can intact; stuck some modern caps inside the chassis...a tight fit, but preserves the aesthetics. Does the plexi AMPEG panel light up? IS the tube cage still there? (Damn, now I want another one...not much power, but TONE for days! (for bass, anyway)
Tom

[Structo]

I had an old Ampeg solid state guitar amp years ago.

It seems maybe it had the name Portaflex or something similar.

It had this cool front panel that was like printed circuit board material that when the power was on, the part that was etched away glowed this cool kind of blue color.

That thing kept blowing power transistors and I finally gave up on it.

[stompjunkie]

Thanks for the advice about the decoupler cap Selloutrr. I'll try that first.

Tube Tek- It's an all octal amp (I really like 6sl7's) this one is built on a circuit board though. It has almost everything original...it's missing the plexiglass logo plate. It's a shame because it's one of the coolest parts of the amp. Oh well, it should still sound great when it's up and running. Oh thats a great idea using the old cap shell for cosmetics, I may have to give that a try....

Ampeg made so many cool amps. I don't know why they never caught on as well as fender or marshall.... I've got a gemini I that I absolutely love. It's every bit as nice as my 65 deluxe reverb, just with a diferent character. I've also had really good luck before with a VT-40 that sounded better than most supers out there.... Oh well, more for us in the know then! You can still get these really cheap with a little looking around....