Squealing Amp - Dodgy Service Job?

cormacdaly · 02:15 PM

Hi Guys,

First post here. I just had a service job done on a Blackheart BH5 guitar amp. I had blown the output transformer by playing at full blast with a full band a little too often (oops haha).

So I decided to try out a different OT that I had seen recommended by a few different sites - a Hammond 125ESE.

Following the job the amp is really noisy and squealing quite badly as I turn up the volume. The actual pitch of the squeal changes as I turn up the volume.

I thought maybe it could be the new valves, but when I opened up the amp I could see that the OT was slightly off axis from being 90 degrees perpendicular to the Power Transformer.

[IMG]

[/IMG]

Hopefully the above link works.

Could this be responsible for the noise that I'm hearing?

cormacdaly · 19th December 2012, 02:48 PM

Ha. For some reason my entire thread has just disappeared.

I just had a new Output Transformer installed, and my BH5 guitar amp hasn't stopped squealing since.

Here's a pic of the install job:

Any advice?

Frank Berry · 19th December 2012, 03:00 PM

They may have wired the transformer primary backwards. Swap the primary wires and see what happens.

Hi-Q · 04:01 PM

Frank has a good point as wiring the primary (or secondary for that matter) the wrong way will invert the feedback signal and cause this problem. A big presumption though that this amp uses what should be negative feedback, bearing in mind it is a guitar amp built more for raw grunt than audio perfection. But as this problem has only occurred since changing the OT then a very valid point and worthy of a check. The howling varying with the volume control certainly steers ones thoughts in this direction. Just another thought though, isn't that output Tranny a little close to the ECC83 on the input? I know it has a screening can, it's just that it doesn't seem right somehow, let's say I would not have designed the layout in that way. Les

kevinkr · 19th December 2012, 04:13 PM

Please post all guitar amplifier threads to Instruments & Amplifiers per forum policy. See sub headers at the top of each forum for the explanation.
Please don't post duplicate threads, duplicate deleted.

19th December 2012, 02:05 PM	#1
cormacdaly diyAudio Member Join Date: Dec 2012	Squealing Amp - Dodgy Service Job? Hi Guys, First post here. I just had a service job done on a Blackheart BH5 guitar amp. I had blown the output transformer by playing at full blast with a full band a little too often (oops haha). So I decided to try out a different OT that I had seen recommended by a few different sites - a Hammond 125ESE. Following the job the amp is really noisy and squealing quite badly as I turn up the volume. The actual pitch of the squeal changes as I turn up the volume. I thought maybe it could be the new valves, but when I opened up the amp I could see that the OT was slightly off axis from being 90 degrees perpendicular to the Power Transformer. [IMG][/IMG] Hopefully the above link works. Could this be responsible for the noise that I'm hearing? Last edited by cormacdaly; 19th December 2012 at 02:15 PM.

19th December 2012, 03:00 PM	#3
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	They may have wired the transformer primary backwards. Swap the primary wires and see what happens. __________________ Frank

19th December 2012, 03:57 PM	#4
Hi-Q diyAudio Member Join Date: Oct 2007	Frank has a good point as wiring the primary (or secondary for that matter) the wrong way will invert the feedback signal and cause this problem. A big presumption though that this amp uses what should be negative feedback, bearing in mind it is a guitar amp built more for raw grunt than audio perfection. But as this problem has only occurred since changing the OT then a very valid point and worthy of a check. The howling varying with the volume control certainly steers ones thoughts in this direction. Just another thought though, isn't that output Tranny a little close to the ECC83 on the input? I know it has a screening can, it's just that it doesn't seem right somehow, let's say I would not have designed the layout in that way. Les Last edited by Hi-Q; 19th December 2012 at 04:01 PM.

19th December 2012, 04:13 PM	#5
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Please post all guitar amplifier threads to Instruments & Amplifiers per forum policy. See sub headers at the top of each forum for the explanation. Please don't post duplicate threads, duplicate deleted. __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

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


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

19th December 2012, 02:48 PM	#2
cormacdaly diyAudio Member Join Date: Dec 2012	Ha. For some reason my entire thread has just disappeared. I just had a new Output Transformer installed, and my BH5 guitar amp hasn't stopped squealing since. Here's a pic of the install job: Any advice?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Amp won't stop squealing?????	soadx12	Car Audio	2	10th September 2010 09:28 AM
In dire need of help with a "squealing" amp.	istari knight	Solid State	8	10th March 2010 04:12 PM
dodgy amp power supply	obaka-san	Parts	1	9th January 2008 09:12 AM
dodgy riddle - problems repairing an amp	meezger_seep	Solid State	16	23rd July 2007 08:11 PM
Dodgy amp needs repair	sbattersby 115	Instruments and Amps	13	29th April 2005 09:33 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