----- Original Message -----

From: Darren T. Brown

To: hammond_zone@...

Sent: Saturday, April 28, 2001 12:58 PM

Subject: Re: Hum (was Re: [hammond_zone] Power Supply Info)

The Chelmer Valve company is an excellent UK source for new and tested tubes, they are very reasonable and use only highest quality tubes. They supply me with valves for the 122 Leslie and XB3. Also I have purchased replacement valves for L and M series spinets from them. You can buy matched pairs too.

?

?

Darren

----- Original Message -----

From: Gren

To: hammond_zone@...

Sent: Saturday, April 28, 2001 9:38 AM

Subject: Re: Hum (was Re: [hammond_zone] Power Supply Info)

Thanks for the info Jeff..

?

I didn't realise the 5U4 was a directly heated cathode .. I know now. .. I was getting it mixed up with the 5X4 which is.

?

I'm in Birmingham UK but I do come to the US every year on vacation. (we drove across the US last year).. so getting a tube from the US is not a problem. I (like the M) have lots of contacts in the US who could get the tubes and send them. I just never thought of it .. (DUH!)

?

Whats the best way of measuring the hum from the output of the caps ?

The 'hum' being only a small proportion of the output voltage.

?

You have been a great eye opener. I only have limited tech knowledge but have worked with tubes way back in the days of the 807 power amp .. when the 6V6 was used as a driver.. oh those were the days.? LOL

?

Thanks again

Gren

?

Want to know about potbellied pigs ?
Meet Bushka at ......

----- Original Message -----

From: Jeff Dairiki

To: hammond_zone@...

Sent: Friday, April 27, 2001 5:13 PM

Subject: Hum (was Re: [hammond_zone] Power Supply Info)

>My M101 has had a hum for some time and although I replaced the large
>electrolytics and the rectifier bottle (sorry tube) I still cant get rid of
>it .. With a great deal of care I have measured the output from the
>cathode of the rectifier and I suspect I have a heater to cathode leakage.

Why do you say that?? (Do you mean heater to cathode leakage in the
rectifier?? That doesn't make sense --- the 5U4 does not have a
separate cathode: the header is the cathode.)? (If you mean heater-to-cathode
leakage in some other tube, that could well be the cause of your hum
(see below.))

Are you sure the hum is coming from the preamp/amp?? Does the swell pedal
affect the hum volume?? Does the hum get better/worse as the preamp warms
up?? If you ground the inputs to the preamp, what happens?

If you're sure the hum is coming from the (pre)amp I'd check the rest of
the tubes, particularly the finals.?? If you can get your hands on known
good spares, the best thing to do is swap them out one at a time (except
swap the finals as a pair).

See also

>Not having a clue how to check that I wondered if it was worth (or even
>dangerous) to use a bridge instead of the old bottle rectifier.

You can, but that's a whole nuther kettle of fish --- IMHO, it's
not worth the effort and worry.? If you just replace the rectifier
with a pair of diodes, your B+ voltage will go up (probably
doing bad things.)? Also the rest of the tubes see full B+ will before
their cathodes are warmed up: this is known to be bad for the life
of the tubes ("cathode stripping").??? So you need to at least add a resistor
(to drop some voltage) in series with the diodes, and possible add some other
stuff to delay the "turn-on" of the B+ supply.

>I have having difficuly getting hold of good quality valves
>and the last replacement I tried in it started to spark over on power up.

They shouldn't be that hard to find (though you probably will need to resort
to mail order.)? Where are you located?? If you're near the US, see:
?
for several good sources of tubes.?

Sparks are definitely bad :-) --- either that tube was already bad (or was
one of the real el-cheapos) --- or it might indicate further troubles
with your amp.

Jeff

PS Note to Guillermo who's thinking of buying a Trek preamp to cure hum in
his A-105:

I've heard nothing but good about the Trek preamps.? Nevertheless, replacing
the preamp solely to fix hum seems rather extreme.? Unless you're absolutely
sure the hum is coming from the preamp, it might not even fix the problem.
Why not just fix the preamp (or have it fixed)?





Visit The Hammond Zone


To unsubscribe from this group, send an email to:
hammond_zone-unsubscribe@...



Your use of Yahoo! Groups is subject to the .

Visit The Hammond Zone


To unsubscribe from this group, send an email to:
hammond_zone-unsubscribe@...



Your use of Yahoo! Groups is subject to the .

Visit The Hammond Zone


To unsubscribe from this group, send an email to:
hammond_zone-unsubscribe@...



Your use of Yahoo! Groups is subject to the .