Problem with old Heathkit

-=Zepplock=- · 17th June 2006, 04:30 AM

Hello All,

I have an old Heathkit tube amp which is all original and was working OK. Couple of days ago I noticed some noise on left channel.

The noise is like a rumble. Like a thunder but very low. Left channel only. The volume control does NOT affect the noise. The noise pattern is like 5-10 sec of silence then 2-3 seconds noise.

I moved all tubes around (swapped left/right) - and it still comes from left channel.
The mono/stereo/reversedstereo/reversedmono does NOT affect the noise.

Do you think this is a transformer?

SY · 17th June 2006, 11:39 AM

Doubtful. Far more likely to be a coupling cap, a bypass cap, or a solder joint in the left power amp section.

Geek · 17th June 2006, 12:15 PM

Before pulling her apart, swap output tubes. If the rumble is still in the left channel, look for bad solder joints and/or recap. If it switches channels, new tubes.

-=Zepplock=- · 17th June 2006, 06:57 PM

Quote:

Originally posted by Geek
Before pulling her apart, swap output tubes. If the rumble is still in the left channel, look for bad solder joints and/or recap. If it switches channels, new tubes.

I did that. It is still in the left channel.

p.s. I would be so happy if it was a tube ;-) Cheap and easy to replace.

-=Zepplock=- · 17th June 2006, 07:00 PM

Quote:

Originally posted by SY
Doubtful. Far more likely to be a coupling cap, a bypass cap, or a solder joint in the left power amp section.

Here is a schematics: link

where are those caps?

anatech · 17th June 2006, 07:17 PM

Hi Zepplock,
The louder the noise is, the closer to the input of the amplifier stage is will generally be. Don't discount the old carbon composition resistors for making noise either.

There are two tests you can make here. The first is to measure the ends of each coupling cap. The side going to the grid of the next tube should measure 0 VDC, within mV. The other test is to measure the resistor values after the supplies are discharged. You may find some out of tolerance. Take the time to match the 47K phase splitter resistors. Replace the parts that are out of tolerance.

I'd be replacing the coupling capacitors anyway if I were you.

-Chris

tubelab.com · 17th June 2006, 07:37 PM

Quote:

Don't discount the old carbon composition resistors for making noise either.

I second that! I have seen resistors make a rumbling or frying sound. It can also be a tube socket, but those will usually behave for a few days after changing the tubes.

You say that the function switch does not affect the noise, so that puts the problem in the area of the 6AN8 or the 6BQ5's.

The coupling caps are C19 and C21 for A channel and C44 and C45 for B channel. If they have never been replaced I would change them. The health of your output tubes depends on them.

I have often been able to find intermittent resistors with "freeze spray", although the freeze spray is getting hard to find. When the amp is making the noise, CAREFULLY spray each resistor one at a time, and wait for a few seconds. Often the bad resistor will behave when it is thermally shocked.

List of suspects: R24, R25, R26, R28, R30. Also the same resistors in the other channel. It is not clear from the schematic which is the left channel.

poobah · 17th June 2006, 07:38 PM

What you are describing SURE sounds like a solder joint or resistor. It is behaving exactly like the old blinker relays for turn signals. Heat from current causes the joint to open... once it opens the current wanes... as does the heat... and the joint reconnects. It could even be a tube socket... likely that would have a more severe impact on sound though.

Anatech is dead on the money, recap that old dog regardless; if you wish to keep it. Failing caps can fry transformers, tubes, all sorts of things. If you are SERIOUS, we can make a list of the caps you should service.

Caps died in my Leslie amp/speaker not too long ago... I had it unplugged in about 1/2 a second.

2nd Edit: I can't type in lttle boxes!!!!!!!!!!!!

anatech · 17th June 2006, 07:46 PM

Hi poobah,

Quote:

I can't type in lttle boxes!!!!!!!!!!!!

I'm sure we can find you some bigger boxes to type in. We didn't think of wookies, sorry. Why would you want to type in a little box anyway??

-Chris

poobah · 17th June 2006, 08:18 PM

It seems that I can never see the missing words, words I type twice, spelling... until I post!

17th June 2006, 04:30 AM	#1
-=Zepplock=- diyAudio Member Join Date: Mar 2005 Location: Sunnyvale, CA	Problem with old Heathkit Hello All, I have an old Heathkit tube amp which is all original and was working OK. Couple of days ago I noticed some noise on left channel. The noise is like a rumble. Like a thunder but very low. Left channel only. The volume control does NOT affect the noise. The noise pattern is like 5-10 sec of silence then 2-3 seconds noise. I moved all tubes around (swapped left/right) - and it still comes from left channel. The mono/stereo/reversedstereo/reversedmono does NOT affect the noise. Do you think this is a transformer? __________________ Led Zeppelin Forever Make Love Not War

17th June 2006, 11:39 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Doubtful. Far more likely to be a coupling cap, a bypass cap, or a solder joint in the left power amp section. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
heathkit crossover xo-1 / x0-1 problem	SOFIA1999	Parts	0	12th November 2008 04:53 PM
Heathkit W-5M	rajacat	Tubes / Valves	7	15th October 2007 06:51 PM
Heathkit AA-100	imix500	Tubes / Valves	2	28th December 2005 09:35 PM
Heathkit EA-2	Hewie	Tubes / Valves	6	14th October 2003 06:41 PM
Heathkit SW-717	phoshious	Parts	9	4th July 2002 03:05 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

17th June 2006, 12:15 PM	#3
Geek diyAudio Member Join Date: Sep 2004	Before pulling her apart, swap output tubes. If the rumble is still in the left channel, look for bad solder joints and/or recap. If it switches channels, new tubes.

17th June 2006, 07:17 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Zepplock, The louder the noise is, the closer to the input of the amplifier stage is will generally be. Don't discount the old carbon composition resistors for making noise either. There are two tests you can make here. The first is to measure the ends of each coupling cap. The side going to the grid of the next tube should measure 0 VDC, within mV. The other test is to measure the resistor values after the supplies are discharged. You may find some out of tolerance. Take the time to match the 47K phase splitter resistors. Replace the parts that are out of tolerance. I'd be replacing the coupling capacitors anyway if I were you. -Chris

17th June 2006, 07:38 PM	#8
poobah diyAudio Member Join Date: Nov 2005	What you are describing SURE sounds like a solder joint or resistor. It is behaving exactly like the old blinker relays for turn signals. Heat from current causes the joint to open... once it opens the current wanes... as does the heat... and the joint reconnects. It could even be a tube socket... likely that would have a more severe impact on sound though. Anatech is dead on the money, recap that old dog regardless; if you wish to keep it. Failing caps can fry transformers, tubes, all sorts of things. If you are SERIOUS, we can make a list of the caps you should service. Caps died in my Leslie amp/speaker not too long ago... I had it unplugged in about 1/2 a second. 2nd Edit: I can't type in lttle boxes!!!!!!!!!!!!

17th June 2006, 08:18 PM	#10
poobah diyAudio Member Join Date: Nov 2005	It seems that I can never see the missing words, words I type twice, spelling... until I post!

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)