Hi, all out there....
I can see that there is some talk around QUAD II amplifiers from
1960's.
I have 3 of those amplifiers. I have tested them and all works. But I
don't have tubes to all of them. So I have to move around the tubes to
have the amplifiers checked.
Do You think there is some value in these 3 amp's???

They have been used by the Swedish Television as control-rooms
amplifiers.
There seems to have some modifications at the input. There is a
transformer at the input, so there is a balanced input, instead of the
ordinary unbalanced input.

About the tubes (it uses KT77 for the output-stage), can I use EL34 (I
have some of those)?
I know that I have connect pin 1 and 8 to get them running.
But will it reduce the value?

OK.....I think I stop there, and see if someone reply on this.

Bo-Lennart Karlsson
SWEDEN

"Bo-Lennart"

I can see that there is some talk around QUAD II amplifiers from
1960's.
I have 3 of those amplifiers. I have tested them and all works. But I
don't have tubes to all of them. So I have to move around the tubes to
have the amplifiers checked.
Do You think there is some value in these 3 amp's???


** Good examples go for high prices on eBay.


They have been used by the Swedish Television as control-rooms
amplifiers.
There seems to have some modifications at the input. There is a
transformer at the input, so there is a balanced input, instead of the
ordinary unbalanced input.


** Original condition is best for sale value.


About the tubes (it uses KT77 for the output-stage),


** The Quad 2 uses KT66s ( or 6L6GTs ) and these give the best results.

KT77s (or EL34s ) cannot be used unless extensive internal modifications
are in place to compensate for the different bias and gain of that tube.

Seems your Quad 2s are heavily modified.




....... Phil

On 27 Sep, 03:46, "Phil Allison" wrote:
"Bo-Lennart"



I can see that there is some talk around QUAD II amplifiers from
1960's.
I have 3 of those amplifiers. I have tested them and all works. But I
don't have tubes to all of them. So I have to move around the tubes to
have the amplifiers checked.
Do You think there is some value in these 3 amp's???

** Good examples go for high prices on eBay.

They have been used by the Swedish Television as control-rooms
amplifiers.
There seems to have some modifications at the input. There is a
transformer at the input, so there is a balanced input, instead of the
ordinary unbalanced input.

** Original condition is best for sale value.

About the tubes (it uses KT77 for the output-stage),

** The Quad 2 uses KT66s ( or 6L6GTs ) and these give the best results.

KT77s (or EL34s ) cannot be used unless extensive internal modifications
are in place to compensate for the different bias and gain of that tube.

Seems your Quad 2s are heavily modified.

...... Phil

Thank's Phil for Your reply.
Well, there is labeled on the chassie "KT77". But , as You mentioned,
on all schematics I found on the net, they all show KT66.
I also found that the resitor R12 is at 150 ohm instead of the 180 ohm
that are stated everywhere.
But do You think that could be a modification to get the right bias
for that KT77?

That's the only change that I can see concerning the original
schematics.
Well, about the input modification. (transformer at the input). It
seems that it might have been done at the factory.
Do You think the Swedish Television ordered a custom-tailored
version???

OK.......let see if there is more reply's coming in.

Thank's Phil

Bo-Lennart Karlsson
SWEDEN

"Bo-Lennart"

** Original condition is best for sale value.

About the tubes (it uses KT77 for the output-stage),

** The Quad 2 uses KT66s ( or 6L6GTs ) and these give the best results.

KT77s (or EL34s ) cannot be used unless extensive internal modifications
are in place to compensate for the different bias and gain of that tube.

Seems your Quad 2s are heavily modified.


Well, there is labelled on the chassie "KT77".


** So what - did you see who labelled it so ??



But , as You mentioned,
on all schematics I found on the net, they all show KT66.
I also found that the resistor R12 is at 150 ohm instead of the 180 ohm
that are stated everywhere.
But do You think that could be a modification to get the right bias
for that KT77?


** May well be the only mod done.


That's the only change that I can see concerning the original
schematics.

** OK.


Well, about the input modification. (transformer at the input). It
seems that it might have been done at the factory.


** Just as unlikely as the theorising that Quad did the KT77 mod.

Far more likely is that some tech at the TV station did it.


Do You think the Swedish Television ordered a custom-tailored
version???


** Go ask them.


OK.......let see if there is more reply's coming in.


** The substitution of KT77s for KT66s is no improvement to the Quad
- KT66s being the more linear tube in that amp. THD figures goes up by 4
times or more when EL34s are substituted, even with the bias adjusted.

Buy some good KT66s and put that cathode resistor back to 180ohms.

Then try them on eBay.



........ Phil

In article .com,
Bo-Lennart wrote:
Well, about the input modification. (transformer at the input). It
seems that it might have been done at the factory.
Do You think the Swedish Television ordered a custom-tailored
version???

Quad were happy to supply their amps with balanced inputs for pro use.
With the '3' range they made the 50 - a single amp in a 303 case with
transformers in and out. Or at least the 100 volt line one had an output
transformer - not too sure about the low z version, but I think it had.

--
*Seen it all, done it all, can't remember most of it*

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)"


Quad were happy to supply their amps with balanced inputs for pro use.


** ********.


With the '3' range they made the 50 - a single amp in a 303 case with
transformers in and out.


** A completely separate product to the famous 303.

Not a domestic hi-fi amp at all - but a rugged, mono PA amplifier.



Or at least the 100 volt line one had an output
transformer - not too sure about the low z version, but I think it had.


** There was only one version.

It drove nearly any impedance load via an OT.

The input tranny was a option.




......... Phil

"Dave Plowman (News)" wrote in message
...
In article .com,
Bo-Lennart wrote:
Well, about the input modification. (transformer at the input). It
seems that it might have been done at the factory.
Do You think the Swedish Television ordered a custom-tailored
version???

Quad were happy to supply their amps with balanced inputs for pro use.
With the '3' range they made the 50 - a single amp in a 303 case with
transformers in and out. Or at least the 100 volt line one had an output
transformer - not too sure about the low z version, but I think it had.

Hei Bo-Lennart. It probably wasn't a custom-tailored version for
STV but a model with Sowter balanced line transformers type 3575
sold to broadcast companies and studios throughout Europe.
I have seen many of them.

Iain

In article ,
Iain Churches wrote:
Hei Bo-Lennart. It probably wasn't a custom-tailored version for
STV but a model with Sowter balanced line transformers type 3575
sold to broadcast companies and studios throughout Europe.
I have seen many of them.

Quad valve amps for some reason were pretty rare in the BBC - at least in
the TV side. Mainly Leak and Sound Sales. But they certainly made up for
it with the Quad 50 - TV theatre in Shepherds Bush, now The Empire, had
over a dozen of them in the early '70s.

--
*Letting a cat out of the bag is easier than putting it back in *

Dave Plowman London SW
To e-mail, change noise into sound.