Taking my Quad II’s to Graeme and finding out they are totally original and untouched since 1964 when they were purchased by the previous and original owner.
Great chat with Graeme (Valvebloke), top bloke.
Thanks Bob (the cheque’s in the post !). It was great to see you too - I hope all the driving wasn’t too painful.
Here’s a pic of the underside of the amps. The only change that’s been made since they left the factory is that the speaker tappings on the output transformer have been re-jumpered from 15ohms down to 8ohms (they were shipped at 15ohms because no-one in their right mind would use any speaker other than the ESL57, would they).
You might just be able to see that the silver Hunts coupling caps in the centre of the right-hand amp carry the date code YIT. For a while the solution to this code was forgotten. Then a few years ago some of us got together on a vintage radio forum to try to recover it. The fact is that Hunts wanted a code that they could read easily but which wouldn’t be obvious to their customers (perhaps so they could resist being asked for the newest possible components ?). They looked for a ten-letter word with no repeated letters which they could use to encode the digits 1 through to 0. They chose WHITSUNDAY. So YIT corresponds to 034. I’ve seen enough Quad IIs that I was able to correlate the cap date codes with another date code on the smoothing block and also with the amps’ serial numbers. It appears that almost all the Hunts caps use the first two digits for the production week and the last one for the final digit of the year. So YIT is week 03, 1964. Irritatingly though, just once in a while I will come across a cap (never, to be fair, of the sort used in Quad IIs) which instead of using the Wk Wk Yr code uses Yr Wk Wk instead. Often there’s a distinct gap between the Yr letter and the Wk ones. But not always. Ho hum.
Hope the KT66s are working well in the new amps
Would you replace them just because they are over 50 years old and likely to have issues, or do you test them?
First thing to say is that I ‘keep’ everything. I never cut leads when I take a component out of circuit. That way a future owner can always put them back.
I’m very reluctant to keep either the coupling caps or the KT66 cathode cap. At best the latter dries out and becomes useless. At worst it explodes and/or shorts out. If it shorts then the KT66s turn hard on and it’s pot luck as to what goes bang first (sadly it’s often the mains transformer HT winding, but it could be the output transformer primary and even if they survive it won’t do the KT66s any good either). Likewise the coupling caps very often go leaky (electrically). This may happen quite suddenly and without warning, so testing isn’t much help. Equally it may only show up when they have hundreds of volts across them and have got properly warm. It often drives one of the KT66s into red-plating thermal runaway which again can take out the mains transformer or the output transformer.
I tend to replace the Mouldseal cap between the EF86 screen grids too. The insulation on the outside of this is prone to cracking (often so badly that big lumps fall off). Moisture gets in and the cap deteriorates. There may be no immediately audible effect (although the distortion will have risen significantly). But if either of the EF86s should start to decline then things can get a lot more exciting. The plastic insulation on the Mouldseals really stinks when it gets hot.
The resistors all creep high in value. This upsets the amp’s balance. I can replace them or I can retain them (which can be worth doing if they’re all original, as here) and pad them back down to their correct values with neutral metal film ones slipped in underneath them.
With care the smoothing blocks almost always reform fine. Without care (i.e. just switching the amps on after many years of disuse) they go bang irreparably, sometimes blowing the rectifier too.
I test the valves in circuit and if they’re still good (they often are) I keep them, juggling them around so that small offsets in some are compensated, as far as possible, by small but opposite offsets in others. Sadly KT66s which haven’t been used fairly regularly are often prone to going ‘gassy’. This can be a real pain to try to deal with and treatment is by no means always successful.
Should do, not in them yet, just delivered the amps yesterday to Graeme. I didn’t want to switch on the amps until they were tested, in case things went boom, as they have not been used since 1985.
Wise move - certainly not worth taking the risk
A post was merged into an existing topic: Bob’s new wagon
Bob's new wagon
“It was all a swirl of drugs and drinking …”. You don’t say !
Nice nap this afternoon. A welcome break from the summer cough / cold. 8/10
Bob's new wagon
Just found out that a growth my father has is not cancerous. He’s had three unrelated cancers, and treatment has cured all of them - he’s had surgery, radiotherapy, chemotherapy, proton beam therapy, you name it. He’s alive thanks to the NHS, but I doubt he’d want to get yet more treatment!
My mother is a “cured” cancer patient - whatever the NHS did to her and her Ovarian cancer 15 years ago was truly miraculous
How one man built a $51m theme park for his daughter - http://www.bbc.co.uk/news/magazine-40742586
Probably worthy of a thread of their own.
The discipline, pride and bloody professionalism of these guys makes me well up. Loved them ever since I first saw them as a kid.
Shit music tho.