Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chocopower on March 03, 2011, 03:06:22 am

Title: Noise with new power transformer.
Post by: chocopower on March 03, 2011, 03:06:22 am

Hi,

i friend of mine had installed a new power transformer with 240vac primary to replace the 120v one. Amp is a AB165 Bassman.
the new trafo is a hammond 290 EEX.
Amp is working, but with this strange noise. He send me a video.

http://www.megaupload.com/?d=JE14ONCS (http://www.megaupload.com/?d=JE14ONCS)  (sorry for the 45 secons wait...   :embarrassed:)

At first he think the new trafo could be the culprit, so he talk with the supplier and them send a new one without extra charge. (nice guys, Tubetown).
he installed the new one... and the same problem....
He tried the original 120v one and the amp work without noises...

He live far away from me, so i have no way to test the amp.
Next step is:
.- send me a good pic of the internals
.- measure voltajes in the whole amp

any other idea?

Title: Re: Noise with new power transformer.
Post by: kagliostro on March 03, 2011, 05:24:03 am

How he test the amp with the 120v standard transformer ?

does he used a Variac, an autotransformer or may be a 220v / 120v transformer ?

if he used a 220v / 120v transformer I suggest to try the new one with a 220v / 220v isolation transformer as to verify if the noise disappear

the old transformer has a shield connection that the new one didn't has ?

were the wires soldered with a good ground scheme ?

Kagliostro

p.s.: to mee seems a neon lamp noise, perhaps ............. turning off the light that can be easily verified .......

Title: Re: Noise with new power transformer.
Post by: chocopower on March 03, 2011, 07:35:16 am

How he test the amp with the 120v standard transformer ?
does he used a Variac, an autotransformer or may be a 220v / 120v transformer ?
He used a 220v / 120v transformer.

if he used a 220v / 120v transformer I suggest to try the new one with a 220v / 220v isolation transformer as to verify if the noise disappear
I´ll tell him about this test.

the old transformer has a shield connection that the new one didn't has ?
the specs are there:
 http://www.tube-town.net/ttstore/product_info.php/info/p2180_Hammond-290EEX-Fender-Power-125P7D---022814-Bassman.html (http://www.tube-town.net/ttstore/product_info.php/info/p2180_Hammond-290EEX-Fender-Power-125P7D---022814-Bassman.html)
Seemes the Hammond have a shield c.

were the wires soldered with a good ground scheme ?
I dont know. I´ll post the pics when he send it to me.

p.s.: to mee seems a neon lamp noise, perhaps ............. turning off the light that can be easily verified .......
I agree with you. that kind of noise  seems to be from an external source, but the fact the old trafo work without problems get me crazy!


thank a lot for your help!!

Title: Re: Noise with new power transformer.
Post by: kagliostro on March 03, 2011, 07:53:24 am

May be I'm TOTALLY wrong BUT

Quote

He used a 220v / 120v transformer.

I supposed !

Quote

I agree with you. that kind of noise  seems to be from an external source, but the fact the old trafo work without problems get me crazy!

the 120v old transformer was connected thru the 220v / 120v transformer which give a galvanic isolation from the wall wart

I Hope that the 220v / 220v transformer will give some positive result

I'm waiting with you

Kagliostro

Title: Re: Noise with new power transformer.
Post by: kagliostro on March 13, 2011, 05:29:21 am

I've just find, in another tread, here in the forum, this link

http://www.ebtechaudio.com/hedes.html

may be it is of interest

did your friend solved the problem ?

Kagliostro

Title: Re: Noise with new power transformer.
Post by: chocopower on March 13, 2011, 02:04:26 pm

Hi!

Cool link! thanks! Maybe i pick one for my self.

I have no news about the problem. Maybe this week...