Thank you for the answer I will measure over the weekend (I hope). The two capacitors are not Hunts, they are Jensen PIOs so I think they should be ok.
Regards,
Predrag
Uff, now you made me restless, (ok it sounds very good so I do not care). Why do you think that? If it is the RCA input it is just a metal plate add on to replace the Jonas connector (that I have, and keep if I want to sell them on in future). Resistors and capacitors have been changed by the previous owner, but looking just at the metalwork this is one old amplifier, and I think it is very hard to fake it.
Regards,
Predrag
Pred,
My mistake then about the capacitors. I did not know Jensen made metal cover caps - the image was just too small to show the logo.
Tinitus,
I would also be interested in why you say that. The resistors have certainly been changed from the previous 20% 'ceramic tube' types as have certain capacitors (I have compunction about that tiny C5, but that later). I did not know there was a later copy version other than the 'classic' one.
My mistake then about the capacitors. I did not know Jensen made metal cover caps - the image was just too small to show the logo.
Tinitus,
I would also be interested in why you say that. The resistors have certainly been changed from the previous 20% 'ceramic tube' types as have certain capacitors (I have compunction about that tiny C5, but that later). I did not know there was a later copy version other than the 'classic' one.
I was also puzzeled at first, but these are Jensen pio Alu foil. Usualy they have orange color but if you take of plastic protection (guy wanted to have some pF to ground as some recomend) then they look like this.
Just when I turn on the amp on my testbench to measure, is it important that there is a load at the speaker outputs, or I can leave them floating?
Regards,
Pred
I also was confused by Tinitus's comment, but then wondered if he was referring to the KT66's rather than the amps as a whole?
I wonder if I might ask you knowledgeable fellows how I might gently awaken my II's after over 10 years of not being powered up? Perhaps a light bulb in line with the mains? I don't have a variac. I really don't want to startle them! They have been sitting on a shelf in a dry and warm room all this time so damp not an issue.
Thanks and regards to all!
Tyron
I wonder if I might ask you knowledgeable fellows how I might gently awaken my II's after over 10 years of not being powered up? Perhaps a light bulb in line with the mains? I don't have a variac. I really don't want to startle them! They have been sitting on a shelf in a dry and warm room all this time so damp not an issue.
Thanks and regards to all!
Tyron
Pred,
You can power up without a load resistor, unless there is something grossly amiss with the amplifier(s). The NFB network places an equivalent 1,6Kohm load on the output from a 16 ohm l.s. viewpoint. If you have a scope you can just verifty. I now understand about the coupling capacitors, but I would at an early stage just verify a 'clean' output with an oscilloscope and square wave generator. The fact that the Hunts had aboout 18pF to common does not mean that others will have it too. I am also somewhat nervous about removing an insulating sleeve; again that does not necessarily mean that one can simply earth the outer metal cover. One might grant that the refurbisher checked that, though.
Tyron,
With tube amplifiers there is no simple answer, because (1) the amplifier may not be stable at part h.t voltage, (2) the heaters would also be operating at a low voltage and conductivity may only start later. Still, when that is the only way .... I usually 'started up' with the tubes removed and two Si diodes replacing the rectifier for the time plus Variac. Should you have access to say two 1N4007 diodes, that will be the best way - lamp in series, all tubes removed. Keep track of things with a voltmeter. (Can you perhaps borrow a Variac?) Best way to track is another temporary dis-connection: Place an ammeter between diodes and first capacitor (since the diodes are 'up-in-the-air' anyway). A steady current after several minutes will be the indication. (In the Quad II there is no resistor shunts across the h.t. to draw extra current.) The reading should be no more than a few micro-amps. But don't switch on with said meter at so sensitive a scale - don't overload the meter!
You can power up without a load resistor, unless there is something grossly amiss with the amplifier(s). The NFB network places an equivalent 1,6Kohm load on the output from a 16 ohm l.s. viewpoint. If you have a scope you can just verifty. I now understand about the coupling capacitors, but I would at an early stage just verify a 'clean' output with an oscilloscope and square wave generator. The fact that the Hunts had aboout 18pF to common does not mean that others will have it too. I am also somewhat nervous about removing an insulating sleeve; again that does not necessarily mean that one can simply earth the outer metal cover. One might grant that the refurbisher checked that, though.
Tyron,
With tube amplifiers there is no simple answer, because (1) the amplifier may not be stable at part h.t voltage, (2) the heaters would also be operating at a low voltage and conductivity may only start later. Still, when that is the only way .... I usually 'started up' with the tubes removed and two Si diodes replacing the rectifier for the time plus Variac. Should you have access to say two 1N4007 diodes, that will be the best way - lamp in series, all tubes removed. Keep track of things with a voltmeter. (Can you perhaps borrow a Variac?) Best way to track is another temporary dis-connection: Place an ammeter between diodes and first capacitor (since the diodes are 'up-in-the-air' anyway). A steady current after several minutes will be the indication. (In the Quad II there is no resistor shunts across the h.t. to draw extra current.) The reading should be no more than a few micro-amps. But don't switch on with said meter at so sensitive a scale - don't overload the meter!
Oh, I didnt think about that, I just thought you knew
I once had a pair of old renovated Quad II
One thing I notice is the painting, it looks brighter, somewhat fresh
And I notice something about the name plate
And I remember the metal work as being a bit more accurate
I look especially at edges on trafo potting
And those small screwing plates fore mounting bottom plate, did they use thos back then
I could be wrong tho
But theres a series number on each amp, so it should be relatively easy
Ahh, seems the later "copy" looks quite a lot more different
Quad - Classic Series - Valve Amps - Quad II-eighty
And the original
d.c.~daylight ltd. — QUAD II Buying —
But looking like that they would be very rare, or renovated
Still, nameplates look slightly different from those I can find, they are all with golden bronze "look", and painted on their backside, and not see through
Though, nameplates could be renovated too
Sorry for inconvenience
I could have checked first
And just fore the fun of it...ebayer selling copies, built in 1978 from original parts
http://cgi.ebay.co.uk/Quad-II-Monob..._HomeAudioHiFi_Amplifiers?hash=item1e5ad26a29
Scroll down and take a close look at that exstreme internal wire work
Well, Im sorry I made this mess
Quad - Classic Series - Valve Amps - Quad II-eighty
And the original
d.c.~daylight ltd. — QUAD II Buying —
But looking like that they would be very rare, or renovated
Still, nameplates look slightly different from those I can find, they are all with golden bronze "look", and painted on their backside, and not see through
Though, nameplates could be renovated too
Sorry for inconvenience
I could have checked first
And just fore the fun of it...ebayer selling copies, built in 1978 from original parts
http://cgi.ebay.co.uk/Quad-II-Monob..._HomeAudioHiFi_Amplifiers?hash=item1e5ad26a29
Scroll down and take a close look at that exstreme internal wire work
Well, Im sorry I made this mess
Attachments
Yes,
Nostalgia again ..... It is mostly a pity about renovations that, with respect, the renovators did not know their jobs. As said, physically over-small C5s, and nobody seems to have really done something about that hot R12 mounted ... as said before. The h.f. peak (though not in the audio band) as a result of a change in C2, C3, etc.
Not to repeat. I understood from the factory that the choke designation was unimportant - I cannot now recall what the difference was. Transformers - not sure why they should deteriorate with age, unless over-driven/over-heated.
The Quad II-40 had the same topology as the original, but I was not happy about the distortion at maximum output not being below 0,4% (specs said 0,3%). I got a rather vague non-explaining reply to that from the factory. I never looked at the recent 'II-80'. To get that power the KT88s must go class AB1 - and with that the output transformer design becomes a little more involved ....
Nostalgia again ..... It is mostly a pity about renovations that, with respect, the renovators did not know their jobs. As said, physically over-small C5s, and nobody seems to have really done something about that hot R12 mounted ... as said before. The h.f. peak (though not in the audio band) as a result of a change in C2, C3, etc.
Not to repeat. I understood from the factory that the choke designation was unimportant - I cannot now recall what the difference was. Transformers - not sure why they should deteriorate with age, unless over-driven/over-heated.
The Quad II-40 had the same topology as the original, but I was not happy about the distortion at maximum output not being below 0,4% (specs said 0,3%). I got a rather vague non-explaining reply to that from the factory. I never looked at the recent 'II-80'. To get that power the KT88s must go class AB1 - and with that the output transformer design becomes a little more involved ....
Hello all,
As you helped a lot I would feel embarrassed not to do a thing. So last night although tired from chasing kids all day, changing dippers I took some time to measure I was more cautious than ever in my life, even one hand at the back
I found 336 volts on HT and 330 after the choke, so bang on. Ef86 grids are a bit off they are like on 103 and other 91. I think it is since they are not matched, Mullards are more older then Valvos. Before the capacitor on the anode of EF86 I have 121 and 110, not bad. Cathode resistor on KT66 is at 23.3 V a bit of so I have like 130mA for two tubes. I would guess that the 180Ohm resistor is getting hot and more resistive.
What I am worried about is blazingly hot 180Ohm resistor and for the moment I do not have a good idea where to fit it. I think that the choke is hot just by a chimney effect from this resistor since After 10-20mins it is so hot you can not touch it. Do you have some pics of your setups ? I took some and will try to prepare something and reread your suggestions to come up with the idea.
Second I measure 0.3V (around 250mV) on the grids of the KT66, is this normal? I know that the resistors are not going directly to ground so this is why I ask.
Finally resistors are off by 10%-20% I do not like it but will change when I have more time and find some good replacements.
Anyway the amp is for sure genuine. When you look the lettering and inside it is so full of age that you would need a lot of money to fake that.
Did anyone try 6l6wgb in this amp. Specs are the same as KT66 only thing is that there is maximum voltage of 400V?
And finally how much of the power supply rise (I wanted to write VDD, damn integrated circuits at work ) if I replace GZ32 with GZ34, I found one for a reasonable price and wanted to buy just to try?
Best regards,
Pred
As you helped a lot I would feel embarrassed not to do a thing. So last night although tired from chasing kids all day, changing dippers I took some time to measure
I was more cautious than ever in my life, even one hand at the back I found 336 volts on HT and 330 after the choke, so bang on. Ef86 grids are a bit off they are like on 103 and other 91. I think it is since they are not matched, Mullards are more older then Valvos. Before the capacitor on the anode of EF86 I have 121 and 110, not bad. Cathode resistor on KT66 is at 23.3 V a bit of so I have like 130mA for two tubes. I would guess that the 180Ohm resistor is getting hot and more resistive.
What I am worried about is blazingly hot 180Ohm resistor and for the moment I do not have a good idea where to fit it. I think that the choke is hot just by a chimney effect from this resistor since After 10-20mins it is so hot you can not touch it. Do you have some pics of your setups ? I took some and will try to prepare something and reread your suggestions to come up with the idea.
Second I measure 0.3V (around 250mV) on the grids of the KT66, is this normal? I know that the resistors are not going directly to ground so this is why I ask.
Finally resistors are off by 10%-20% I do not like it but will change when I have more time and find some good replacements.
Anyway the amp is for sure genuine. When you look the lettering and inside it is so full of age that you would need a lot of money to fake that.
Did anyone try 6l6wgb in this amp. Specs are the same as KT66 only thing is that there is maximum voltage of 400V?
And finally how much of the power supply rise (I wanted to write VDD, damn integrated circuits at work
) if I replace GZ32 with GZ34, I found one for a reasonable price and wanted to buy just to try?Best regards,
Pred
I think those amps MAY have been serviced by Keith Snook. He does the same thing with the original name plates (rubbing the paint off the back) as shown at the bottom of this page:
QUAD II Valve Power Amplifier Modernising and Modifying
I can't tell from your photo but it looks like the green resistor under the choke is a 5W Kiwame job? In which case it is good quality, but might benefit from some kind of addition heatsinking. Failing that a heatsinked 180-Ohm wirewound resistor would be worth fitting for peace of mind:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=1073942
- John
P.S. Regarding KT66s the Shuguang KT-66R (R for retro) are based on an original KT66 valve which was sacrificed to enable the design phase of this valve. I used them for 3 years with no problem at all. It IS Chinese, but made to a UK spec I believe:
Tube-Shop.com - Vacuum Tubes for Hi-Fi, Guitar and Radio amplifiers
The Gold Lion KT66 is also meant to sound fantastic:
Gold Lion KT66
QUAD II Valve Power Amplifier Modernising and Modifying
I can't tell from your photo but it looks like the green resistor under the choke is a 5W Kiwame job? In which case it is good quality, but might benefit from some kind of addition heatsinking. Failing that a heatsinked 180-Ohm wirewound resistor would be worth fitting for peace of mind:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=1073942
- John
P.S. Regarding KT66s the Shuguang KT-66R (R for retro) are based on an original KT66 valve which was sacrificed to enable the design phase of this valve. I used them for 3 years with no problem at all. It IS Chinese, but made to a UK spec I believe:
Tube-Shop.com - Vacuum Tubes for Hi-Fi, Guitar and Radio amplifiers
The Gold Lion KT66 is also meant to sound fantastic:
Gold Lion KT66
Last edited:
Pred,
Some of your questions were answered in my posts #36 and #39, and others. As said, 6L6GCs could be used with advantage.
I looked at the 'DC - daylight" site. OK, the guy does say "modernising and modifying" but I prefer to just restore (refurbish, whatever). Using a Quad II chassis and components in another circuit no longer constitutes a "Quad II". If the wiring is quite different ... well, one can argue, I suppose. With due respect, the wiring of the worthy author of the above site was untidy. Did it make a difference to the sound - probably not. Did it make a difference to the character - definitely. I would not purchase his Quads.
But enough of that. The arguable R12-C5. Heavy weather is often made of 'the smallest dc influencing low frequency response (of the OPT); or effect of tube unbalance. May we just take a look at the original specs (1955 Quad booklet page 21): "Valve mismatching up to 25% (introducing 2nd harmonic) not to cause distortion to exceed 0.18%. Total distortion at 25 c/s not to exceed 0.25%.".
I have found that among some 30 6L6GCs or WXTs, the spread in plate current at 75mA was no more than 8%. Among EH 6L6GCs it was down to
6% and among 12 Tung-Sol 6L6GC-STRs, 5%.
I use a quite higher C5-value not for stability reasons. At maximum output the Ia will increase, even though one has class-A conditions. Under signal conditions a high enough C5 will simulate fixed bias conditions; tube data shows the improvement. That is why I use 2200µF (35V) for C5. (That is the one change I will confess to.)
Regarding R12 it was mentioned that you could move it to where C5 is situated at present, and mount C5 across the present tie tags. Keep R12 in the air; I use a 10W type which distribute heat somewhat more evenly because of its size. To repeat: Keep R12 away from C5 and from under the choke.
If not mentioned before, the h.t. voltage will rise to about 355V by using a GZ34. This is still within the maximum dissipation ratings - 25W for KT66, 30W for 6L6GC.
Some of your questions were answered in my posts #36 and #39, and others. As said, 6L6GCs could be used with advantage.
I looked at the 'DC - daylight" site. OK, the guy does say "modernising and modifying" but I prefer to just restore (refurbish, whatever). Using a Quad II chassis and components in another circuit no longer constitutes a "Quad II". If the wiring is quite different ... well, one can argue, I suppose. With due respect, the wiring of the worthy author of the above site was untidy. Did it make a difference to the sound - probably not. Did it make a difference to the character - definitely. I would not purchase his Quads.
But enough of that. The arguable R12-C5. Heavy weather is often made of 'the smallest dc influencing low frequency response (of the OPT); or effect of tube unbalance. May we just take a look at the original specs (1955 Quad booklet page 21): "Valve mismatching up to 25% (introducing 2nd harmonic) not to cause distortion to exceed 0.18%. Total distortion at 25 c/s not to exceed 0.25%.".
I have found that among some 30 6L6GCs or WXTs, the spread in plate current at 75mA was no more than 8%. Among EH 6L6GCs it was down to
6% and among 12 Tung-Sol 6L6GC-STRs, 5%.
I use a quite higher C5-value not for stability reasons. At maximum output the Ia will increase, even though one has class-A conditions. Under signal conditions a high enough C5 will simulate fixed bias conditions; tube data shows the improvement. That is why I use 2200µF (35V) for C5. (That is the one change I will confess to.)
Regarding R12 it was mentioned that you could move it to where C5 is situated at present, and mount C5 across the present tie tags. Keep R12 in the air; I use a 10W type which distribute heat somewhat more evenly because of its size. To repeat: Keep R12 away from C5 and from under the choke.
If not mentioned before, the h.t. voltage will rise to about 355V by using a GZ34. This is still within the maximum dissipation ratings - 25W for KT66, 30W for 6L6GC.
Can't sleep, I'll be regretting it tomorrow at work
was happy reading your replies. Well with GZ34 it will come to 24W a lot close to maximum dissipation, now I am not sure if I even should try it with my GEC tubes?
I was asking about some NOS 6l6wgb since they are cheaper (I guess guitar people can not use them). Did you notice much of a sound change with 6l6gc?
I saw some 180 thick film resistors that look like TO220 package. I thought it would be not bad to screw them to the chassis using rectifier socket, but I guess your examples are easier to implement... I see that resistors are not that expensive so I will have to wait some time to collect enough of "things" so shipping will not hurt. I will listen for the moment hour or so.
My worry about 300mV at KT66 grids is no more. I read dc-daylight site and he writes it is perfectly ok. So I will leave it for the moment, find some nice resistors and order them to replace all of them in the amp, just to feel more comfortable.
Thank you guys again for help and I will report if I do something new (I replaced RIFA's that I have with some Vishay MKP1836 I think, no more difference but I feel more relaxed since it is a better capacitor).
Regards,
Pred
was happy reading your replies. Well with GZ34 it will come to 24W a lot close to maximum dissipation, now I am not sure if I even should try it with my GEC tubes?
I was asking about some NOS 6l6wgb since they are cheaper (I guess guitar people can not use them). Did you notice much of a sound change with 6l6gc?
I saw some 180 thick film resistors that look like TO220 package. I thought it would be not bad to screw them to the chassis using rectifier socket, but I guess your examples are easier to implement... I see that resistors are not that expensive so I will have to wait some time to collect enough of "things" so shipping will not hurt. I will listen for the moment hour or so.
My worry about 300mV at KT66 grids is no more. I read dc-daylight site and he writes it is perfectly ok. So I will leave it for the moment, find some nice resistors and order them to replace all of them in the amp, just to feel more comfortable.
Thank you guys again for help and I will report if I do something new (I replaced RIFA's that I have with some Vishay MKP1836 I think, no more difference but I feel more relaxed since it is a better capacitor).
Regards,
Pred
Pred,
Oh - yes ... forgot that the rest of the world is not as fortunate as us having a public holiday tomorrow!
No difference in sound. The circuit topology irons out a lot of small differences, as demonstarted by quoting the specs. The dissipation comes to 22W total. Remember that Va is between anode and cathode, and that total current includes screen also.
And I might make some enemies, but don't waste money on over-expensive boutique brand components. E.g. polyester/polycarbonate capacitors are quite fine. [I will not upset members by touching on the 'audio quality' (sic) legends.]
Wishing you well with your venture!
PS: Wise words by Stevieg.
Oh - yes ... forgot that the rest of the world is not as fortunate as us having a public holiday tomorrow!
No difference in sound. The circuit topology irons out a lot of small differences, as demonstarted by quoting the specs. The dissipation comes to 22W total. Remember that Va is between anode and cathode, and that total current includes screen also.
And I might make some enemies, but don't waste money on over-expensive boutique brand components. E.g. polyester/polycarbonate capacitors are quite fine. [I will not upset members by touching on the 'audio quality' (sic) legends.]
Wishing you well with your venture!
PS: Wise words by Stevieg.
R12 resistor type
After looking into my amp I am now convinced that the R12 is responsible for the choke high temperature. I want to change it but am not so sure on how to approach this.
What I like a lot are thick metal film resistors like these ones, and are not sooo expencive, 12$ a piece.
Arcol NPR2 TO-221
and I look for the place to bolt them since they need heat sinking. I indetified two transformer screws that could be used for the job, like in my picture. What do you think about them?
I must add I like metalic ones wirewound but they seem heavy to be hanging from the leads for a long time. What types you guys use? Can someone send some photos just to have an idea?
Regards,
Pred
After looking into my amp I am now convinced that the R12 is responsible for the choke high temperature. I want to change it but am not so sure on how to approach this.
What I like a lot are thick metal film resistors like these ones, and are not sooo expencive, 12$ a piece.
Arcol NPR2 TO-221
and I look for the place to bolt them since they need heat sinking. I indetified two transformer screws that could be used for the job, like in my picture. What do you think about them?
I must add I like metalic ones wirewound but they seem heavy to be hanging from the leads for a long time. What types you guys use? Can someone send some photos just to have an idea?
Regards,
Pred
Attachments
Hi Pred,
Very nice resistors indeed! We down here in RSA are not priviledged to have that kind of thing stocked locally. But it is unnecessarily sofisticated. I have used ww resistors similar to the type mounted there at present (a 10W version). There is also the possibility that a 25W Arcol might simply be used without heatsink, as the dissipation is about 3W only. Perhaps someone else can advise whether you could mount the Arcol without heatsink in this case.
If you do make that move, the best place could be the rectifier tube socket screw where C5 is situated at present. The contact area will be limited because of the limited socket tab area, but as said above. The screw (one of two) holding down the choke again brings heat a little closer to the choke, but not as seriously as before.
Hanging a 10W resistor by the leads is no problem. If you are worried, perhaps wind the leads a turn or so round the terminal before soldering. (And that little C5 shown in your photo, is rather scrawny. Try get a larger type, higher capacitance as explained before.
Very nice resistors indeed! We down here in RSA are not priviledged to have that kind of thing stocked locally. But it is unnecessarily sofisticated. I have used ww resistors similar to the type mounted there at present (a 10W version). There is also the possibility that a 25W Arcol might simply be used without heatsink, as the dissipation is about 3W only. Perhaps someone else can advise whether you could mount the Arcol without heatsink in this case.
If you do make that move, the best place could be the rectifier tube socket screw where C5 is situated at present. The contact area will be limited because of the limited socket tab area, but as said above. The screw (one of two) holding down the choke again brings heat a little closer to the choke, but not as seriously as before.
Hanging a 10W resistor by the leads is no problem. If you are worried, perhaps wind the leads a turn or so round the terminal before soldering. (And that little C5 shown in your photo, is rather scrawny. Try get a larger type, higher capacitance as explained before.
Just a few notes... I did read some of the posts above, but beeing a newbie here on Diy there is so much to read.
I own a pair of Quad II's and they are my main source. I have fixed them up and learned a few things along the way, some even from Erik Andersson (Audion etc).
1) KT66 original GEC are the best tubes for the Quad II. I have tried a number of alternatives before I stumbled on a fair supply of early 1970's made in original boxes - all GEC. They are snappier and they are cleaner.
2) Capacitors. They need to be changed to modern ones. I even had a breakdown of the big double one, so I carved it out and mounted modern capacitors in the old box. Looks good!
3) GZ32. Not GZ34. Erik was very specific about that, but I do not remember what his point was. As I happened to have two new Mullard from the 60's in original boxes, I took the 34's out and put original 32's in. Anyway, he looked at the spec for 34 and said that the 32 is a much better fit, regardless of power handling and the like (I trust him).
4) Tube matching. I matched all my KT66's (a few in the box) in pairs and use two pairs that where in the same range. Same with the EF86's - match them!
5) Resistors. I took out all resistors carefully and measured them before storing them. New metal film ones went in. Some values of the original ones were off by 30%...
6) Tube sockets. Put new ones in and lots of crackle and noise disappears.
I do not think that there is much sense in modifying the design itself - it's pretty good.
My Quad II's currently drives a pair of Yamaha NS1000M's in mint condition. Great combination. I also have a pair of mini monitors with Lowther DX2 with the PM6 cone assembly. Fantastic speakers and a perfect match to the Quad II's!
All the best to all, and keep them Quad II's in good shape!
/p
I own a pair of Quad II's and they are my main source. I have fixed them up and learned a few things along the way, some even from Erik Andersson (Audion etc).
1) KT66 original GEC are the best tubes for the Quad II. I have tried a number of alternatives before I stumbled on a fair supply of early 1970's made in original boxes - all GEC. They are snappier and they are cleaner.
2) Capacitors. They need to be changed to modern ones. I even had a breakdown of the big double one, so I carved it out and mounted modern capacitors in the old box. Looks good!
3) GZ32. Not GZ34. Erik was very specific about that, but I do not remember what his point was. As I happened to have two new Mullard from the 60's in original boxes, I took the 34's out and put original 32's in. Anyway, he looked at the spec for 34 and said that the 32 is a much better fit, regardless of power handling and the like (I trust him).
4) Tube matching. I matched all my KT66's (a few in the box
) in pairs and use two pairs that where in the same range. Same with the EF86's - match them!5) Resistors. I took out all resistors carefully and measured them before storing them. New metal film ones went in. Some values of the original ones were off by 30%...
6) Tube sockets. Put new ones in and lots of crackle and noise disappears.
I do not think that there is much sense in modifying the design itself - it's pretty good.
My Quad II's currently drives a pair of Yamaha NS1000M's in mint condition. Great combination. I also have a pair of mini monitors with Lowther DX2 with the PM6 cone assembly. Fantastic speakers and a perfect match to the Quad II's!
All the best to all, and keep them Quad II's in good shape!
/p
Just found this old thread and decided to add my twopence-worth.
I have a pair of Quad II kindly given to me by an old friend, They were modified by Guy Croft and further by me.
Croft's modifications were in the power supply; there are silicon diodes and a 6080 pass valve controlled by a pair of ecc83s which are crammed underneath. The 180 ohm cathode resistor has been suitably uprated. The amplifiers arrived fitted with EL34s which I do not think are a good idea - partly because the need 1.5A fpr their heaters. I refuse to pay stupid money for GEC ones. Once upon a time there was in Crystal Palace a TV Repair shop; he had lots of brand-new EL 37s at 15/- each (75p)
Anyway as he's gone I chose Russian 5881s and also 6L6GCs; they are excellent and best of all all the voltages are spot on and they draw only 0.9A for their heaters. I'm delighted with them. Next I took Chris Beeching's advice an replaced the EF86s with Brimar's 6BR7s a little rewiring of the bases and changing a resistor or two gave good audible improvement,
I have built a rather unusual preamplifier which uses four RCA955 acorn triodes; these are DC coupled to 6AW8A triode pentodes, the triodes being cathode followers and the pentodes their loads, Itested the prototype and the frequency response was -3dB at 177kHz The 955s configured as diff pairs were tested for distortion with very good results. Tested as they are to be run, THD was around -55dB 0.15% delivering +35dBU
When I get the Quads back I should like to replace the input circuitry with a triode diff pair. For the valves I would like to use I would need 35-40mA can I steal this? I'll be removing the 6080 and the two ECC83s of course and I'll build some 317 regulators and there'll be a standby switch too. My chosen valve will give gain of about 20 and as my line stage gives 20 I should be well away.
Paul
Finally I have some STC 5B/255M, these are Loctal based 807s; they may well go in...
Well they're modified already.
I have a pair of Quad II kindly given to me by an old friend, They were modified by Guy Croft and further by me.
Croft's modifications were in the power supply; there are silicon diodes and a 6080 pass valve controlled by a pair of ecc83s which are crammed underneath. The 180 ohm cathode resistor has been suitably uprated. The amplifiers arrived fitted with EL34s which I do not think are a good idea - partly because the need 1.5A fpr their heaters. I refuse to pay stupid money for GEC ones. Once upon a time there was in Crystal Palace a TV Repair shop; he had lots of brand-new EL 37s at 15/- each (75p)
Anyway as he's gone I chose Russian 5881s and also 6L6GCs; they are excellent and best of all all the voltages are spot on and they draw only 0.9A for their heaters. I'm delighted with them. Next I took Chris Beeching's advice an replaced the EF86s with Brimar's 6BR7s a little rewiring of the bases and changing a resistor or two gave good audible improvement,
I have built a rather unusual preamplifier which uses four RCA955 acorn triodes; these are DC coupled to 6AW8A triode pentodes, the triodes being cathode followers and the pentodes their loads, Itested the prototype and the frequency response was -3dB at 177kHz The 955s configured as diff pairs were tested for distortion with very good results. Tested as they are to be run, THD was around -55dB 0.15% delivering +35dBU
When I get the Quads back I should like to replace the input circuitry with a triode diff pair. For the valves I would like to use I would need 35-40mA can I steal this? I'll be removing the 6080 and the two ECC83s of course and I'll build some 317 regulators and there'll be a standby switch too. My chosen valve will give gain of about 20 and as my line stage gives 20 I should be well away.
Paul
Finally I have some STC 5B/255M, these are Loctal based 807s; they may well go in...
Well they're modified already.
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