Dear Forum!
After some years of thinking about those units, I've finally bought a set of mine.
These are coming from the UK (from the only and the first owners) the preamp from a different source, but also in a very good state.
All the three looks fairly well cosmetically, un-abused and free of any rust. Tubes are factory ones in the IIs, but not original in the 22's (one Brimar three Mullards, one of them from Holland)
My plan is to use them with my QUAD ESL 57's, but as they are in an untouched, factory condition, I am sure they need a huge refurb.
As far as I know from some respectable forumers here at Hungary, that the end-amps are something those are really sings even these days in a modern setup, but preamp has rather a museal value than a real use-value as they are inferior in quality for HiFi, but I want to use them, together, as they are a set, and I would like to have an as authentical system as I could possibly have.
So far, I have found a lot of information regarding these amps, so I decided to refurb them (or rather just have them set up) by myself.
My questions are, if it is possible to have these repairs at home by me, who's have only a marginal knowledge regarding the subject, but having good soldering skills, a DVM, a cap checker, a 100W light bulb, 230V mains and a registered profile at Mouser and eBay?
Thank you for your answers, help and encouragements in advance! 😉
After some years of thinking about those units, I've finally bought a set of mine.
These are coming from the UK (from the only and the first owners) the preamp from a different source, but also in a very good state.
All the three looks fairly well cosmetically, un-abused and free of any rust. Tubes are factory ones in the IIs, but not original in the 22's (one Brimar three Mullards, one of them from Holland)
My plan is to use them with my QUAD ESL 57's, but as they are in an untouched, factory condition, I am sure they need a huge refurb.
As far as I know from some respectable forumers here at Hungary, that the end-amps are something those are really sings even these days in a modern setup, but preamp has rather a museal value than a real use-value as they are inferior in quality for HiFi, but I want to use them, together, as they are a set, and I would like to have an as authentical system as I could possibly have.
So far, I have found a lot of information regarding these amps, so I decided to refurb them (or rather just have them set up) by myself.
My questions are, if it is possible to have these repairs at home by me, who's have only a marginal knowledge regarding the subject, but having good soldering skills, a DVM, a cap checker, a 100W light bulb, 230V mains and a registered profile at Mouser and eBay?
Thank you for your answers, help and encouragements in advance! 😉
Congratulations on your Quads!
The way you have presented this, it's more about you than the amps. How much do you trust your understanding of tube circuits? I would suggest that before attempting any repairs you should read A LOT about basic tube theory. I would suggest Morgan Jones book Valve Amplifiers which you can read many times and refer to constantly. But there is a lot online now as well.
I would say the first step is to get a proper engineer to look at the amp and preamp first, connect it up and check all the voltages against the schematic. Also look at the state of the resistors and capacitors and probably replace some. This might have been done in the amp and preamp already.
That makes your job easier. You now have working equipment. As your knowledge increases and allows, you can then start substituting better parts if you wish, or at least use properly checked original type parts.
The way you have presented this, it's more about you than the amps. How much do you trust your understanding of tube circuits? I would suggest that before attempting any repairs you should read A LOT about basic tube theory. I would suggest Morgan Jones book Valve Amplifiers which you can read many times and refer to constantly. But there is a lot online now as well.
I would say the first step is to get a proper engineer to look at the amp and preamp first, connect it up and check all the voltages against the schematic. Also look at the state of the resistors and capacitors and probably replace some. This might have been done in the amp and preamp already.
That makes your job easier. You now have working equipment. As your knowledge increases and allows, you can then start substituting better parts if you wish, or at least use properly checked original type parts.
Replace all dried capacitors and you are mostly done.
Dear Andy,
Thank you for your reply. I will look after this book, as I only have some knowledge of how the tubes work via Youtube and those old demonstration videos (like this, for example) but that's it.😛 But if someone could give me point to point checklist, which voltages should I check and where (and more specifically, how, if I must disconnect them or not), which ones I should immediately dispose of I think it could work. But that's my opinion, of course, I do not want to melt down anything because of my negligence or jeopardize myself or anyone because of HT
Thank you for your reply. I will look after this book, as I only have some knowledge of how the tubes work via Youtube and those old demonstration videos (like this, for example) but that's it.😛 But if someone could give me point to point checklist, which voltages should I check and where (and more specifically, how, if I must disconnect them or not), which ones I should immediately dispose of I think it could work. But that's my opinion, of course, I do not want to melt down anything because of my negligence or jeopardize myself or anyone because of HT
You could start with connecting them as-is , use them for a while if possible, then you will have a audible reference when tampering with them .
You might not even need to do anything ( except new KT66 tubes), a safer and cheaper way of enjoying your quads!
You might not even need to do anything ( except new KT66 tubes), a safer and cheaper way of enjoying your quads!
I can't wait to start these up, but this bring up questions. Wouldn't make any irreversible problems, if I give it a try? Should I connect a current limiter to them?
And also, I read somewhere that these adapters for the preamp is mandatory, if I want to connect anything to them ...
And also, I read somewhere that these adapters for the preamp is mandatory, if I want to connect anything to them ...
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A 60w bulb in series doesn't hurt for the first time. Try and grab the voltages to ground for all the tube pins, and post them here. Then some tests like feeling transformers for heat, and you're good to go.
There are some good tips for sympathetic enhancements on Patrick Turner's site, who sadly passed away recently.
There are some good tips for sympathetic enhancements on Patrick Turner's site, who sadly passed away recently.
Thank you for your tips! This sounds eerie, but fun! I will try to operate it with the bulb, for the first time. My mains rated 230V. How to calculate the suitable W of the lightbulb? Is 60W enough, or 100W even better?
Will I need these plug-in-the-back-of-the-preamp adapters to feed a nowday's line level to the 22's?
Will I need these plug-in-the-back-of-the-preamp adapters to feed a nowday's line level to the 22's?
I have recently refurbished my own pair of IIs and have attempted to bring two 22s into service.
The IIs are pretty easy. Go slow, take your time, and double-check your work. I wouldn’t even think of applying power if they have the original Hunts coupling caps in them. Those need to go, fast. Also check the values of R12 and C5; they are underspecced and poorly placed so the resistor drifts from heat, and the capacitor dries out from being too close to the resistor. You’ll probably want to bump the watt rating of the resistor when you replace it.
Check the wiring of the output transformer. Many of them come from the factory set at 16 ohms; you’ll need to change some jumpers for 8.
In one of my two the big can cap had failed. They will almost certainly need attention, but you can probably get by on a dim bulb with them.
You will probably be tempted to “modernize” them when you realize the power plugs and audio input won’t really run without the 22, due to the way the ground runs through the 6 pin connector, while mains is distributed through just two-prong plugs. You will see a lot of people fitting IEC connectors and RCA inputs, but this means cutting the chassis.
What I did was to get two of the 6-pin to RCA adapters available on e-bay for audio input, and create two mains plugs with the earth connection on the lead tied to the case screw. This means I can use them with other input sources without cutting the case. When I get the 22s running, I’ll be able to use them without undoing some of the modernizing.
Speaking of the 22s you will probably find they require a lot more work. The hard parts are checking and redoing the tone controls (the caps are awful and way out of spec), getting to the components on the “top” side of the switching mechanism to test and replace the
, and figuring out what to do about the can cap, which nobody seems to make in that size anymore. I have also had a lot of trouble with the volume / balance / power controls. Both of them were bad in mine, and I’m having real problems sorting out replacements that fit.
Other things to know: GZ32s put out lower voltage than GZ34s, but it’s hard to find new 32s, so your tubes might run a bit hotter using 34s. The consensus seems to be that this is OK though.
You might think about putting plastic screws in the holes for the unused voltage selectors, since they have mains voltage on them and they might be tempting targets for tiny fingers, if you have any small humans around.
Don’t tube roll with these. You’ll find lots of bad advice about putting KT88s in them, but unless you’re absolutely certain that the other tubes will draw the same HT and heater current, it’s probably best to stick with 66s. The heater windings on the PT are famously “fragile” so you may find yourself shopping for a new PT if you don’t observe the heater ratings.
Ignore most things on the Patrick Turner pages, IMO. He basically put a different amp in the same chassis. Keith Snook has lots of really great advice, but you’ll probably need to read it five or six time for it to sink in.
Have fun!
The IIs are pretty easy. Go slow, take your time, and double-check your work. I wouldn’t even think of applying power if they have the original Hunts coupling caps in them. Those need to go, fast. Also check the values of R12 and C5; they are underspecced and poorly placed so the resistor drifts from heat, and the capacitor dries out from being too close to the resistor. You’ll probably want to bump the watt rating of the resistor when you replace it.
Check the wiring of the output transformer. Many of them come from the factory set at 16 ohms; you’ll need to change some jumpers for 8.
In one of my two the big can cap had failed. They will almost certainly need attention, but you can probably get by on a dim bulb with them.
You will probably be tempted to “modernize” them when you realize the power plugs and audio input won’t really run without the 22, due to the way the ground runs through the 6 pin connector, while mains is distributed through just two-prong plugs. You will see a lot of people fitting IEC connectors and RCA inputs, but this means cutting the chassis.
What I did was to get two of the 6-pin to RCA adapters available on e-bay for audio input, and create two mains plugs with the earth connection on the lead tied to the case screw. This means I can use them with other input sources without cutting the case. When I get the 22s running, I’ll be able to use them without undoing some of the modernizing.
Speaking of the 22s you will probably find they require a lot more work. The hard parts are checking and redoing the tone controls (the caps are awful and way out of spec), getting to the components on the “top” side of the switching mechanism to test and replace the
, and figuring out what to do about the can cap, which nobody seems to make in that size anymore. I have also had a lot of trouble with the volume / balance / power controls. Both of them were bad in mine, and I’m having real problems sorting out replacements that fit.
Other things to know: GZ32s put out lower voltage than GZ34s, but it’s hard to find new 32s, so your tubes might run a bit hotter using 34s. The consensus seems to be that this is OK though.
You might think about putting plastic screws in the holes for the unused voltage selectors, since they have mains voltage on them and they might be tempting targets for tiny fingers, if you have any small humans around.
Don’t tube roll with these. You’ll find lots of bad advice about putting KT88s in them, but unless you’re absolutely certain that the other tubes will draw the same HT and heater current, it’s probably best to stick with 66s. The heater windings on the PT are famously “fragile” so you may find yourself shopping for a new PT if you don’t observe the heater ratings.
Ignore most things on the Patrick Turner pages, IMO. He basically put a different amp in the same chassis. Keith Snook has lots of really great advice, but you’ll probably need to read it five or six time for it to sink in.
Have fun!
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You may also find this video interesting: Valve Amplifier Study 022: Quad II Vintage British Hi-Fi Amplifier - YouTube
Thank you for all your information, and thorough writing!
I have already seen this video, and watched it about 10 times for better understanding. I like the style of the guy! 🙂
As he and others urges you that grid coupling caps must be swapped, so I ordered some NOS russian PIO caps, there is a word that these are a very good substitute soundwise.
I made these for testing:
I have already seen this video, and watched it about 10 times for better understanding. I like the style of the guy! 🙂
As he and others urges you that grid coupling caps must be swapped, so I ordered some NOS russian PIO caps, there is a word that these are a very good substitute soundwise.
I made these for testing:
I would like to use the together for now, and want to keep them as original, as possible. At Turner's page (that is indeed a very thorough write-up, God bless him wherever he is) the article is more or less about modernise these amplifiers, that I am not keen on doing.
Just I want to use the set as regularly as possible, without any problems. So, keep as much of the stuff as safely possible.
My questions so far:
1. Is it possible to reform (with patience) the smoothing can in the II's or it's a must-swap?
2. What's the voltage rating of the brown "drop-like" tone control caps int the 22's ? Styroflex/Polypropylene substitutes would be ok?
3. Are the adapters at the back a must-have? if I want an line-level audio input to the 22s?
4. Are all the black HUNTS tend to leak, and need a swapping? In other words; would it last for long from now?
Just I want to use the set as regularly as possible, without any problems. So, keep as much of the stuff as safely possible.
My questions so far:
1. Is it possible to reform (with patience) the smoothing can in the II's or it's a must-swap?
2. What's the voltage rating of the brown "drop-like" tone control caps int the 22's ? Styroflex/Polypropylene substitutes would be ok?
3. Are the adapters at the back a must-have? if I want an line-level audio input to the 22s?
4. Are all the black HUNTS tend to leak, and need a swapping? In other words; would it last for long from now?
I don’t really see much point, personally, in keeping the old filter caps. Maybe they work for another few years, maybe they blow up tomorrow. Much better to replace them when you have it on the bench now so you don’t have to worry about them.
I don’t think the voltage rating of those caps is too important; anything north of 60v would probably be fine, but I had a hard time finding film caps lower than 150v so that’s what I used.
I didn’t use any of the adapters. I tried using the 22 with a line level input and it produced way too much gain already. The IIs work just fine with direct phone in, so I’m not sure Inwould worry too much. The adapters are mostly tone control networks for applying different equalization curves, AFAIK.
The 22 is quite cramped, so heat is a worry. Get yourself a good LCR meter and check the caps you are suspicious of. Personally I didn’t think it was worth the extra mental worry, wondering if it was going to be the next time I turned it on if a 60 year old cap would fail.
I don’t think the voltage rating of those caps is too important; anything north of 60v would probably be fine, but I had a hard time finding film caps lower than 150v so that’s what I used.
I didn’t use any of the adapters. I tried using the 22 with a line level input and it produced way too much gain already. The IIs work just fine with direct phone in, so I’m not sure Inwould worry too much. The adapters are mostly tone control networks for applying different equalization curves, AFAIK.
The 22 is quite cramped, so heat is a worry. Get yourself a good LCR meter and check the caps you are suspicious of. Personally I didn’t think it was worth the extra mental worry, wondering if it was going to be the next time I turned it on if a 60 year old cap would fail.
If you want to keep them original looking it is possible to stuff new caps in the old cans. Possible, but not easy.
You might find these pages interesting:
Dr. G. Visco; official home page; HiFi rebuild, Quad II
~ QUAD II Amplifier C4 & C6 Replacement PSU Capacitors ~
Rap on Replacing Electrolytic Capacitors
Dr. G. Visco; official home page; HiFi rebuild, Quad II
~ QUAD II Amplifier C4 & C6 Replacement PSU Capacitors ~
Rap on Replacing Electrolytic Capacitors
There is a solution to this without surgery. I fitted a socket for an IEC C5 cable (laptop style), and it fits nicely through the fuse hole. I did drill two small screw holes for my change, but it is possible to anchor to the transformer above and the baseplate below, if you are a purist.
I removed the possibility to change voltages, and an illuminated on/off switch and fuse holder fit nicely in that space. I added a small fillet to meke the plate flush to the hole, and ensure the two items were firmly anchored.
I also drilled one more hole on the side close to the IEC adaptor for a dedicated earch connection. This seperates ground and safety earth, and the amps are completely silent.
Putting the power in by the transformer removes the need to run the mains lead from the front to the back.
STC 5B/255M are a great substitute for the KT66, if NOS and your wallet are concerns, and I have Russian 6K32N on one of the amps, and they seem fine too!
The two unsightly holes were driled by its former owners, Sverige Radio. They had masses of them, and they converted them all to silicon rectification so they could squeeze a few more watts out of them. I bought 4 of them from an ex-Sverige Radio guy, and the other two have factory fitted cages and a rack style base so they can be hot swapped. All 4 had had all passives replaced by SR during their lives. The guy said he had around 3000 KT66 pulls from when the radio station amps were being maintained, but he was old and Corona fears put an end to our socialising.
Another big stash of Quad IIs came from Telia, Sweden's national telecomunications company. They were used for repeater amps, and they have special line output transformers that don't suit loudspeakers, so it is worth being careful when you see unrestored quads for sale, or non-descript transformers for sale. (Information about that on Keith Snook's site).
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