Quad II work

[Arkless Electronics]

For those not wishing to DIY it I offer a full repair and rebuild service for all major brands of vintage valve and SS amplifiers.

 

[chiily]

Very stupid question, but this is all new to me, but are Jones connectors keyed at all?

I've made a couple of Jones to phono leads and I noticed that the Jones connector will only go in one way up. So I assume they are, but there is nothing obvious on the plug or socket itself to key with.

Ta

 

[Barrymagrec]

If I remember correctly the 6 pin jones used on Quads has one end pair of pins further away from the centre than the other so they cannot be inserted wrongly.

Try not to get it the wrong way round or you will put 6.3 volts AC into the output of your preamp.....

 

[chiily]

If I remember correctly the 6 pin jones used on Quads has one end pair of pins further away from the centre than the other so they cannot be inserted wrongly.

Try not to get it the wrong way round or you will put 6.3 volts AC into the output of your preamp.....

I've wired signal and ground to pins 1 and 2, maybe not in that order

 

[chiily]

A little bit more progress this evening.

I ordered a full set of replacement Takman Carbon Film resistors (1W) from HiFi Collective, apart from the 1M ones as they weren't in stock. I've just spent a pleasant evening firstly measuring the resistors in cct, unsoldering each one and checking again. I was aiming only to replace those which were outside of their specification.

Quad 77885 now looks like this:

PXL_20211215_202410303 by Garf Arf, on Flickr

Weird, but the tag to the left of R3, that's the resistor to the right, directly below the 0.1uf black cap, was broken when I got to it. I noticed at the base of the tag a large blob of solder. "I'll get that solder sucker on that!". Heated up the solder and watched the tag fall over. I put it back as best I could without getting too carried away.

And as a little test, can you spot the other, manufacturing error on the board? It must have been there since the amp was built in 1967. I'll give you a clue, it is on one of the bases of the EF86s...and I'm not saying which. Answer at the end

Quad 78079 now looks like this:

PXL_20211215_195300156 by Garf Arf, on Flickr

Understandably the 180k (R5 and R6) resistors were all north of 210k in both amps, one getting to 263k. R7 in 77885 being 900R rather than 680R.

I swapped those outside their design tolerances and kept the rest in service.

Other news: I've bought a set of valves from Watford Valves. Paid today, hopefully they will arrive before Christmas. Also, Keith Snook is sending me a pair of look alike grey metal boxes to replace the PSU and smoothing cap box. I've seen some examples of caps with plastic ties to hold them in place and I don't think that is very sympathetic to the original Quad. Hopefully they will be here by the end of the week.

I also splashed out on some twisted three core, "vintage gold" coloured, cotton covered mains cable to make up the power cables. I think they will look great and the right age for the Quads.

Maybe this weekend I'll start the power up the amps in turn. First through a dim bulb, then with the rectifier, and on wards.

One question is whether valve amps can be run without a load connected to the speaker terminals? I seen various answers on various forums.

And finally....

Whilst I was checking out 7785 I noticed this:

PXL_20211215_203325227 by Garf Arf, on Flickr

It is tricky to spot from the picture. But the cross wire between the EF86s is not soldered to the valve base on the left. I checked the other Quad and it should be soldered. There isn't a hint of solder on the pin at all, so it must have been missed during manufacture. It is hard to tell if the wire is resting against the pin, providing some connection. But not the best...

 

[Barrymagrec]

One question is whether valve amps can be run without a load connected to the speaker terminals? I seen various answers on various forums.

Quads in good condition are unconditionally stable and don`t need a load (according to Quad) but I think after a rebuild it`s quite possible something could go awry and you wouldn`t want to damage the transformers. Suitable wirewound resistors are readily available.

 

[chiily]

Quads in good condition are unconditionally stable and don`t need a load (according to Quad) but I think after a rebuild it`s quite possible something could go awry and you wouldn`t want to damage the transformers. Suitable wirewound resistors are readily available.

That's very useful advice, thank you

I was thinking of powering it up in stages:
No valves - check 5v, 6.3v and transformer HT.
GZ32 in place - check 5v, HT coming out of the GZ32 and HT trace through choke, PSU caps and valve bases.

Could I plug the EF86s in on their own and check their HT and heaters? Ill do that if I can, if not I'll pop all the valves and check voltages as above.

Does that sound like a plan?

My first time with valves

 

[Barrymagrec]

That's very useful advice, thank you

I was thinking of powering it up in stages:
No valves - check 5v, 6.3v and transformer HT.
GZ32 in place - check 5v, HT coming out of the GZ32 and HT trace through choke, PSU caps and valve bases.

Could I plug the EF86s in on their own and check their HT and heaters? Ill do that if I can, if not I'll pop all the valves and check voltages as above.

Does that sound like a plan?

My first time with valves

I would be wary of running without the output valves as the PSU will be very lightly loaded and will put excess volts on the caps and the EF86 stage, offload the HT could rise to 450 volts or more, this would be bad. If you could bring it up on a variac that would be better.

With the KT66s in place you should measure the cathode voltage across R12, this will indicate if they are passing the correct (roughly) current.

You can check the transformer voltages without the valves and you can check the heater voltages without the GZ32. Bear in mind the 5 volts is connected to the HT though this won`t matter without the GZ32 fitted.

 

[Zombie]

There used to be loads about QII on the WAD forum. I don't know if it's still there.

 

[Tony L]

I was thinking of powering it up in stages:
No valves - check 5v, 6.3v and transformer HT.
GZ32 in place - check 5v, HT coming out of the GZ32 and HT trace through choke, PSU caps and valve bases.

Could I plug the EF86s in on their own and check their HT and heaters? Ill do that if I can, if not I'll pop all the valves and check voltages as above.

Does that sound like a plan?

My first time with valves

I’d definitely use a dim-bulb tester for first power on. That will stop any damage if you have a short anywhere. Here’s mine:

It’s documented on my Leak TL12 Plus restoration thread in the classic room. Just a bulb in series. If there is a short the bulb lights up rather than the amp blow up. I used it when recapping the Pass Aleph too, and will do with anything where there is the slightest risk I could have screwed up!

 

[chiily]

Just double checking before powering up...

Tony, I read your Leak thread, really interesting. I've built a dim bulb tester...just in case!

Before powering up the first amp I'm checking continuity between earth and various points. The amp has direct continuity between both 6.3V power transformer taps and earth. I assume that is because of the 6.3V centre tap to earth?

Getting nervous...never done valves before...

 

[Tony L]

The dim-bulb tester takes the risk out for sure, if there is a transformer or wiring issue the bulb will light brightly and stay lit. No harm will come to the amp. I watch a lot of vintage audio restoration stuff on YouTube (XRaytonyB, D-Lab, Electronics Old & New, Mr Carlsons Lab etc) and everyone uses a dim-bulb tester. Most having ones far more complex than mine using a range of different Wattage bulbs that can be switched in or out to allow less or more through. A really simple one like mine will protect you from error on first power-up though. Expect the bulb to glow fairly brightly for a couple of seconds as the rectifier warms up and the caps charge, i.e. don’t panic if it lights! It will flash and then fade to a very low glow. The voltages you measure with it in series will be a bit down on what is expected, but it will certainly give an indication all is ok. The 6.3V is most likely AC so set the meter accordingly (that threw me with the Leaks initially, I made loads of noob errors as you can tell from the thread!).

 

[chiily]

Tony, did you bring your Leaks up with just the rectifier in place or did you pop all the valves in and then try?

 

[chiily]

I should say power applied, no valves. 5VAC at 5.9VAC, 6.3VAC at 6.9VAV, HT at 665VAC... no load though expected to be high...

 

[chiily]

The dim-bulb tester takes the risk out for sure, if there is a transformer or wiring issue the bulb will light brightly and stay lit. No harm will come to the amp. I watch a lot of vintage audio restoration stuff on YouTube (XRaytonyB, D-Lab, Electronics Old & New, Mr Carlsons Lab etc) and everyone uses a dim-bulb tester. Most having ones far more complex than mine using a range of different Wattage bulbs that can be switched in or out to allow less or more through. A really simple one like mine will protect you from error on first power-up though. Expect the bulb to glow fairly brightly for a couple of seconds as the rectifier warms up and the caps charge, i.e. don’t panic if it lights! It will flash and then fade to a very low glow. The voltages you measure with it in series will be a bit down on what is expected, but it will certainly give an indication all is ok. The 6.3V is most likely AC so set the meter accordingly (that threw me with the Leaks initially, I made loads of noob errors as you can tell from the thread!).

Very silly question...how long should I wait for the bulb to die down?

 

[Tony L]

Tony, did you bring your Leaks up with just the rectifier in place or did you pop all the valves in and then try?

IIRC (all with dim-bulb) first nothing just to measure the transformer, then rectifier, then full tube compliment. The dim-bulb acts as a current limiter as well as covering you for shorts. I also have a couple of pretty serious 8 Ohm resistors (the types with metal heat-sinks) bolted to my work-surface to act as a dummy load (not that you need high power capabilities unless you plan to scope it at high levels). I’d certainly stick a load across the speaker outs on any valve amp.

 

[Tony L]

Very silly question...how long should I wait for the bulb to die down?

Only a few seconds, say ten max, though you won’t hurt anything. If it glows bright and stays bright, i.e. as bright as a bulb of that Wattage would be then you have a short somewhere. If all is fine it will glow fairly dully and then fade to next to nothing in a couple of seconds as the rectifier warms up and the caps charge.

PS I’m sure you’ll be fine. Your work looks great and they look like an immaculate pair (I needed superhuman willpower not to buy them myself!). I didn’t make a single mistake in my build, my issue was a broken valve base connector and a couple of noisy NOS carbon resistors. The trouble-shooting is the hard bit with this stuff, that’s where I run out of knowledge real fast. The work itself is easy enough to do neatly and well. @snowman_al and @Radford Revival and others were a huge help and I’m sure will be again if you get stuck. The dim-bulb will certainly prevent catastrophic failure.

 

[chiily]

Thank you for the guidance Tony.

Just tried the rectifier on its own and the bulb is first bright and then dims. Only for maybe 5 secs later for the bulb to re-brighten, to full brightness. I heard a tick from the amp, so turned it off..lol.

 

[Tony L]

Just tried the rectifier on its own and the bulb is first bright and then dims. Only for maybe 5 secs later for the bulb to re-brighten, to full brightness. I heard a tick from the amp, so turned it off..lol.

That’s disturbing. You probably need to consult a grown-up at this point. I wonder if the ‘tick’ could have been the rectifier failing to a short? Did you notice if the rectifier glowed, flashed or sparked or anything?

I’d try it with no valves at all and see if the bulb lights full brightness. That may help establish if it is the amp or the rectifier valve. Some modern rectifiers are just crap.

 

[chiily]

Thank you for the guidance Tony.

Just tried the rectifier on its own and the bulb is first bright and then dims. Only for maybe 5 secs later for the bulb to re-brighten, to full brightness. I heard a tick from the amp, so turned it off..lol.

I think is is normal as the rectifier warms up, it ticks , SS amp don't do that!!!...just checking the DC voltage across the PSU. On the E pin I'm seeing 384V and on the P pin 400V.

PSU is working.

Without the valves in a did test each tag to earth...no continuity.

It doesn't jump out at me.