help with my bassman!

django · 12-23-2008, 10:46 PM

a rebiased it recently and hit a wrong spot which resulted in some sparks, but now the non bright side isn't working(i've tried switching out the caps and valve) and when i play hard or above a certain volume it makes a crackling noise(which isn't the speaker) could this be caused by the power amp valves?

thanks, michael

hasserl · 12-24-2008, 12:00 AM

Since the problem is only with one of the two channels it probably is not the power valves.

django · 12-24-2008, 12:42 AM

sorry didn't explain it very well one channel doesn't work at all, and the other channel becomes really crackly when you play louder or dig in.

txstrat · 12-24-2008, 01:47 AM

I think tube amps and their parts are quite forgiving. If you didn't hold the piece of metal too long to any spot it might spark but shouldn't be of serious harm to the amp. Several of my amps threw sparks while I was troubleshooting or measuring around with a MM tip and took no harm at all.
(this should be no free ticket for fooling around in a tube amp with pieces of metal)
Where exactly did you hit the pcb? or eyelet board? that it threw sparks?
If it's a pcb you might "welded" a bridge between some conducting paths and the signal runs to ground. I would check that for the "no sound" channel.
The crackling (intermittent?) noise could be a bad solder joint. Check everything you soldered again.

django · 12-24-2008, 12:40 PM

i tried measuring the bias current directly and sparks started flying, the amp has been working for a few months but all of a sudden went funny when i did that, but i'll check all the solder joints again! one of the caps from the output of the last preamp stage looks a little singed should i try replacing that?

txstrat · 12-25-2008, 01:04 AM

I would. If there is a hint of burning and you have a replacement handy, I'd go ahead and replace it. What do you have to loose?
1. How exactly did you measure the current with the meter? If you had to loosen up any connections. That's where I'd look first.
2. is it a pcb and are there any tracks of "bridges"?
I don't know how skilled you are. Just be careful - tube amps can be LETHAL

django · 12-28-2008, 03:34 PM

turns out it was the cap on the end of the phase splitter that had gone its working fine now and sounding better than ever! think the same happened on the bass side of the preamp to, may have to order a complete new set of caps as these ones i got given at the course seem unreliable

txstrat · 12-28-2008, 08:13 PM

Thanks for your feedback.
Glad you sorted it out.

django · 01-02-2009, 08:58 PM

okay its started happening again, what could be causing the caps to melt? badly biased valves or could it be the valves on the way out?

Diablo · 01-04-2009, 12:07 AM

Quote:

Originally Posted by django

okay its started happening again, what could be causing the caps to melt? badly biased valves or could it be the valves on the way out?

Too much voltage?
Attach a schematic of your amp and tell us which cap is melting.

12-23-2008, 10:46 PM	#1
django Junior Member Join Date: Dec 2008 Location: sheffield, uk Posts: 9	help with my bassman! a rebiased it recently and hit a wrong spot which resulted in some sparks, but now the non bright side isn't working(i've tried switching out the caps and valve) and when i play hard or above a certain volume it makes a crackling noise(which isn't the speaker) could this be caused by the power amp valves? thanks, michael

12-25-2008, 01:04 AM	#6
txstrat Senior Member Join Date: Mar 2008 Location: Germany Posts: 728	I would. If there is a hint of burning and you have a replacement handy, I'd go ahead and replace it. What do you have to loose? 1. How exactly did you measure the current with the meter? If you had to loosen up any connections. That's where I'd look first. 2. is it a pcb and are there any tracks of "bridges"? I don't know how skilled you are. Just be careful - tube amps can be LETHAL Last edited by txstrat; 12-25-2008 at 01:18 AM. Reason: added content

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12-24-2008, 12:00 AM	#2
hasserl Senior Member Join Date: May 2006 Posts: 717	Since the problem is only with one of the two channels it probably is not the power valves.

12-24-2008, 12:42 AM	#3
django Junior Member Join Date: Dec 2008 Location: sheffield, uk Posts: 9	sorry didn't explain it very well one channel doesn't work at all, and the other channel becomes really crackly when you play louder or dig in.

12-24-2008, 01:47 AM	#4
txstrat Senior Member Join Date: Mar 2008 Location: Germany Posts: 728	I think tube amps and their parts are quite forgiving. If you didn't hold the piece of metal too long to any spot it might spark but shouldn't be of serious harm to the amp. Several of my amps threw sparks while I was troubleshooting or measuring around with a MM tip and took no harm at all. (this should be no free ticket for fooling around in a tube amp with pieces of metal) Where exactly did you hit the pcb? or eyelet board? that it threw sparks? If it's a pcb you might "welded" a bridge between some conducting paths and the signal runs to ground. I would check that for the "no sound" channel. The crackling (intermittent?) noise could be a bad solder joint. Check everything you soldered again.

12-24-2008, 12:40 PM	#5
django Junior Member Join Date: Dec 2008 Location: sheffield, uk Posts: 9	i tried measuring the bias current directly and sparks started flying, the amp has been working for a few months but all of a sudden went funny when i did that, but i'll check all the solder joints again! one of the caps from the output of the last preamp stage looks a little singed should i try replacing that?

12-28-2008, 03:34 PM	#7
django Junior Member Join Date: Dec 2008 Location: sheffield, uk Posts: 9	turns out it was the cap on the end of the phase splitter that had gone its working fine now and sounding better than ever! think the same happened on the bass side of the preamp to, may have to order a complete new set of caps as these ones i got given at the course seem unreliable

12-28-2008, 08:13 PM	#8
txstrat Senior Member Join Date: Mar 2008 Location: Germany Posts: 728	Thanks for your feedback. Glad you sorted it out.

01-02-2009, 08:58 PM	#9
django Junior Member Join Date: Dec 2008 Location: sheffield, uk Posts: 9	okay its started happening again, what could be causing the caps to melt? badly biased valves or could it be the valves on the way out?

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