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Old 19th December 2012, 02:05 PM   #1
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Join Date: Dec 2012
Default 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]Click the image to open in full size.[/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.
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Old 19th December 2012, 02:48 PM   #2
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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:
Click the image to open in full size.

Any advice?
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Old 19th December 2012, 03:00 PM   #3
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They may have wired the transformer primary backwards. Swap the primary wires and see what happens.
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Old 19th December 2012, 03:57 PM   #4
Hi_Q is offline Hi_Q  England
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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.
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Old 19th December 2012, 04:13 PM   #5
kevinkr is offline kevinkr  United States
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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.
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