[[email protected]]

I have a Sondex valve amplifier with matching solid
state pre-amp. It uses 4 KT88s and I believe it is the last of the line
from Radford Audio.

Does anyone have any information about this amp or where I can find
some -as I gather only very few wewre made. In particular information
on adjusting grid bias would be helpful. Each channel has two terminals
ondernearth two pots and a statement that "grid bias should be set to
2V".

It is currently operating on one channel only - swapping the valves
over indicated that they were not the problem/.

It is not very often you come across equipment where nothing can be
found on the net!!

If anyone has instructions/circuit diagrams etc on paper, I would
willingly pay for a photocopy and postage.

Please email me direct on if you have any
information!

If the ex Sondex specialist from Bristol still visits this group please
get in touch

Regards

David

[Sander deWaal]

said:


Does anyone have any information about this amp or where I can find
some -as I gather only very few wewre made. In particular information
on adjusting grid bias would be helpful. Each channel has two terminals
ondernearth two pots and a statement that "grid bias should be set to
2V".


Dunno anything about this amp, but most likely, the 2 V should be
measured over the cathode resistor(s).

Open up the hood and check for defective fuses, burnt resistors etc.
Looks like you're missing the supply voltage for one channel.

Is it a dual-mono amplifier, e.g. each channel has its own power
tranny?
Do the tubes on the defective channel glow?

--
"Due knot trussed yore spell chequer two fined awl miss steaks."

[Tony Pike]

Try http://www.radfordaudio.co.uk/
I have Radford speakers that need help. Good luck, let me know how you make
out

I have a Sondex valve amplifier with matching solid
state pre-amp. It uses 4 KT88s and I believe it is the last of the line
from Radford Audio.

Does anyone have any information about this amp or where I can find
some -as I gather only very few wewre made. In particular information
on adjusting grid bias would be helpful. Each channel has two terminals
ondernearth two pots and a statement that "grid bias should be set to
2V".

It is currently operating on one channel only - swapping the valves
over indicated that they were not the problem/.

It is not very often you come across equipment where nothing can be
found on the net!!

If anyone has instructions/circuit diagrams etc on paper, I would
willingly pay for a photocopy and postage.

Please email me direct on if you have any
information!

If the ex Sondex specialist from Bristol still visits this group please
get in touch

Regards

David

[Tony Pike]

In furtherance, I need help on a Melos TM90-st valve amp, also using
4 KT 88's, using the Radford Studio 90 loudspeakers. I have had no luck in
a schematic, but have made progress to replacing 2 resistors and 1 diode so
that 1 of the 3 fuses doesn't burn out anymore. When the amp is turned on,
in 1 minute one KT 88 gets fire red (Brand new Electro Harminex valves) and
1 6LU8 does the same thing. I turned it off and that's how it sits. Both
these tubes are on the same circut, left bank. Any suggestions as to where I
go from here????
Regards,
Tony.....
"Tony Pike" wrote in message
news:q5y7h.11851$gy2.228@edtnps90...
Try http://www.radfordaudio.co.uk/
I have Radford speakers that need help. Good luck, let me know how you
make out

I have a Sondex valve amplifier with matching solid
state pre-amp. It uses 4 KT88s and I believe it is the last of the line
from Radford Audio.

Does anyone have any information about this amp or where I can find
some -as I gather only very few wewre made. In particular information
on adjusting grid bias would be helpful. Each channel has two terminals
ondernearth two pots and a statement that "grid bias should be set to
2V".

It is currently operating on one channel only - swapping the valves
over indicated that they were not the problem/.

It is not very often you come across equipment where nothing can be
found on the net!!

If anyone has instructions/circuit diagrams etc on paper, I would
willingly pay for a photocopy and postage.

Please email me direct on if you have any
information!

If the ex Sondex specialist from Bristol still visits this group please
get in touch

Regards

David

[Jon Yaeger]

in article _5tah.13271$p9.2292@edtnps82, Tony Pike at
wrote on 11/26/06 10:39 PM:

In furtherance, I need help on a Melos TM90-st valve amp, also using
4 KT 88's, using the Radford Studio 90 loudspeakers. I have had no luck in
a schematic, but have made progress to replacing 2 resistors and 1 diode so
that 1 of the 3 fuses doesn't burn out anymore. When the amp is turned on,
in 1 minute one KT 88 gets fire red (Brand new Electro Harminex valves) and
1 6LU8 does the same thing. I turned it off and that's how it sits. Both
these tubes are on the same circut, left bank. Any suggestions as to where I
go from here????
Regards,
Tony.....



Hard to give sound advice without the benefit of a schematic.

I suspect that coupling caps to the output tubes may be leaky and bad. It's
a good idea to replace all coupling caps in an old amplifier.

Got a way to test the bias?

I'd install 10 ohm resistors on the cathodes of each KT88 which will act
like a fuse and also give you a way to test current by measuring the voltage
across them (e.g. .4V = 40 ma) - assuming the amp is a fixed bias type.

The EH may not be able to handle the current of the older tubes but it is
more likely that you've got a bias issue.

Doesn't seem like you are very experienced in tube amp repair. Best to find
someone in your area who can service tube gear before you hurt yourself or
the amplifier. Any guitar amp service center should be able to figure it
out.

Best regards,

Jon

[J.P.]

On Mon, 27 Nov 2006 03:39:38 GMT, "Tony Pike"
wrote:

Melos TM90
Only thing I could find on it...

http://www.diyaudio.com/forums/showthread/t-87249.html

[Tony Pike]

Thanks J.P. , will look into it.
"J.P." wrote in message
...
On Mon, 27 Nov 2006 03:39:38 GMT, "Tony Pike"
wrote:

Melos TM90
Only thing I could find on it...

http://www.diyaudio.com/forums/showthread/t-87249.html