Quad II set-up Q's

[Doc B.]

Your filter caps are probably shot. Replace all the electrolytic caps before you plug it in again, to much risk of taking out the power transformers. The coupling caps could be bad too.

[JC]

Presumably, the amps themselves were set to the "230V -250V" range you mentioned earlier? 

[tpatton]

It just occurred to me that the 200W rating of the step-up transformers I tried this AM may be too small, despite the fact that the Quad II's are listed at 90W power consumption.  Could I be right?  I could bid on 500W step-up (and down) transformers on eBay right now--maybe I should?  In which case, who'd like to have my present pair of 200W ones for the price of shipping?

[JC]

If your step-ups can put out 200W @ 240VAC, and the amp is rated to consume 90W at around that same Voltage, then you have plenty of margin, I would think.

To be clear, it is a fuse in the step-up transformer that is blowing, but not a fuse in the amp?  What is the rating of the fuse in the step-up transformer, and what is the rating of the fuse in the amp?  Are either of them specified as "slow-blow" or "time delay"?

[tpatton]

I don't think both Quad II's can be in terrible shape if I got music out of one of them, if only briefly.  I plan to put in CL90 inrush surge limiters in both, and to get 500W transformers to replace the 200W ones.  Maybe that will solve the fuse-blowing problem.  Any other ideas?  Are mine any good?

[JC]

It doesn't seem like there is anything there that cannot be solved.  I would still like to hear about the fuses.

Before blowing more fuses or buying bigger step-up transformers, you may want to gin up a way to use the old light-bulb trick which has been used on countless amps:  In your case, you would need to rig a safe way to put a 100 Watt light bulb in series with the 120V input to your step-up transformer.  Rig this with whatever parts you need to make certain that you have NO 120V exposed!

Once you have this safely set up, simply power up an amp.  You should notice the light bulb flare up for an instant as current rushes in, then rapidly fade to a very low glow.  If the light bulb gets bright and stays bright, you will have an indication that the amp is drawing excessive current and needs further attention.

The advantages of this approach are that it involves only a couple of parts from the hardware/home store, and that, if the amp is indeed drawing too much current, the light bulb simply drops more Voltage, thus protecting the amp and even the fuse in most cases.

Post back if I have been unclear about any of this.  Better to ask questions, etc.

[Doc B.]

I'll guess that JC got it right and I misunderstood, that it's fuses in the stepup transformers that are blowing, and not the amps? What current rating are the fuses?

[John Roman]

Have you made progress on the Quad II's?

[Henry's Cat]

I have personally done a complete refurbishment and modifications to a pair of Quad II's. I have modified my pair for operation with 6L6GT tetrodes as KT66's are rare and very expensive.  All resistors were replaced with modern high quality ones and capacitors with MIT Multicaps, Solen polypropylenes and Black Gate. The amplifiers are well worth restoring .

When I got them they had original GEC KT66's tetrodes and one of the pair of amplifiers had faulty output tubes resulting in the plates glowing red a short time after switch on.  Also, a well known fault is the inadequate power rating of R12 (cathode bias resistor for the output tubes) which nearly always fails with age going open circuit or sometimes short circuiting.  This must be replaced with something more powerful like a 10W resistor. Bear in mind that before warm up the amplifiers take a large turn-on current and it will be even higher if operating off a low voltage mains as in the United States.  The manual states a 2A. fuse for 240V operation and 3A. for 95-125V mains.

I don't quite know why you are using step-transformers as the Quad II's have voltage selectors for a wide range of mains voltages.  Is your mains 110V? There are settings for 110V, 115V and 130V.  Note that here in the United Kingdom the two-pin power inlet plugs do not comply with electrical safety regulations and are illegal.  The amplifiers are not earthed! I replaced mine with three pin clover-leaf (C7) plug and sockets and connected the earth wire to the chassis.