Bottlehead Forum
General Category => General Discussion => Topic started by: tpatton on September 27, 2011, 05:11:16 AM
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For use along with my Bottlehead Paramour II's and S.E.X. amps, I just got a pair of antique Quad II's, and need answers to three questions: (A) how do I wire up the RCA jacks I'll install, (B) how do I set the amps for 110-120 VAC, instead of the 220-240 VAC they now seem to be set for, and (C) how do I set the amps for 8 ohms speakers, when they're standardly set for 15 ohms speakers? I hope my getting the Quad II's isn't taken as disloyalty to, or dissatisfaction with, Bottlehead amps--I don't expect the Quad II's to equal the Bottlehead amps, but I'm old enough to have had a pair of Quad II's over 50 years ago, and the pull of nostalgia is very strong.
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I wish I could be some help but have no experience with Quad. I'm sure a search of the net will provide some answers. Keep us posted.
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Keith Snook in the UK has been incredibly helpful, very generous with his time. Check out his website for a lot of interesting stuff: www.keith-snook.info. (If that isn't right, I'll correct it.) I now know how to set up the Quad II's for 4 to 8 ohms speakers, and have learned that I'll have to use external step-up transformers since their power transformer handles 220-240 VAC only. But I can live with that.
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May I suggest, if you can find the right product, that you consider getting a step-up transformer with some way to adjust the output voltage? Not necessarily a complete variac, which can get expensive, but there must be some with a few taps. The Quad is old enough that power line voltages are probably higher than they were when it was designed - they seem to have been drifting upward for a century, with no end in sight. Just a thought.
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In reply to Paul J's useful suggestion, the Quad II itself has three choices of voltage: 190-209, 210-229 and 230-250. I was going to use the middle range--does that sound right? Or should I be conservative and use 190-209? I'm replacing a lot of resistors and film caps, and could use advice on which caps deserve replacement. The layout is very obscure compared with the neat clarity of Bottlehead gear.
The schematic can be found here: http://www.keith-snook.info/Schematics/QUAD%20II%20Schematic.pdf.
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Fascinating! Those guys were just too clever for their own good ... :^)
Sonically, the coupling caps C2 and C3 are probably the most important. But look at the "Note:" on the circuit! Perhaps Mr. Snook has some other notes on this? You would probably need some auxiliary capacitors if you changed the originals. Any idea what the originals are, and whether they are actually in need of improvement?
The power supply capacitors C6 and C4 would probably be worthwhile, and the cathode bypass C5 - also from a reliability standpoint since they are apparently electrolytics. Note also the special current rating on the power supply input capacitor C6. A modern electrolytic rated for switch-mode (high frequency) power supplies would most likely be OK, but a film cap would be superior and might be available in a small enough package these days.
I have no idea how sensitive the screen-grid cap C1 might be - this is the first time I've seen such an arrangement. It should be easy to swap out and you can listen for any difference - I'm just not prepared to guess what if any difference you might hear.
Thanks for sharing the circuit.
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Personally, I think I would get my step-up transformer and measure the Voltage coming out of it. Set the input Voltage on the amp accordingly.
Step-ups are not necessarily precise, and this will also account for your line Voltage.
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Yeah, Jim has a good point. I just bought a 240V true step up transformer for the lab and it runs more like 250V into our stuff, but it works fine -
http://www.ebay.com/itm/230660480158?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 (http://www.ebay.com/itm/230660480158?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649)
A few months before I had purchased what I thought was a reasonably priced (maybe $65? I can't remember) Chinese 120-240V "step up" from a high feedback ebay seller and, frankly, it is a total piece of shit.
http://www.ebay.com/itm/250772700076?ru=http%3A%2F%2Fwww.ebay.com%3A80%2Fsch%2Fi.html%3F_from%3DR40%26_trksid%3Dp3984.m570.l1313%26_nkw%3D250772700076%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1 (http://www.ebay.com/itm/250772700076?ru=http%3A%2F%2Fwww.ebay.com%3A80%2Fsch%2Fi.html%3F_from%3DR40%26_trksid%3Dp3984.m570.l1313%26_nkw%3D250772700076%26_sacat%3DSee-All-Categories%26_fvi%3D1&_rdc=1)
It's so noisy that it is unusable for audio. It sits in the hallway at work while I screw up the courage to put it where it belongs, in the dumpster.
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Thanks everyone for your continuing help. As to Paul J's suggestions, I can't find either C4 or C6, but can see the two points that C6 connects to, and was planning a film cap bypass there. I'll see if I can do the same for C4. Keith Snook wants good caps for C2 and C3, which I'll do, and wants "a 160V extended foil polystyrene capacitor for C1". I don't know what that is, but would an Obbligato Gold Premium, for example, do? Or would something cheaper do as well? C5 is in sight and I was planning a Nichicon, 22 uF, or the like, bypassed with a 1 uF Solen. Should I spend more there?
I was planning to do what Jim suggests on the transformer: measure and set the amp accordingly. I hope my inexpensive step-up transformers prove to be okay--ordered on eBay but not here yet.
I'm going to change every resistor in sight, may of which don't measure very close to proper values.
Thanks again for all the help--I consider this now to be a joint project, and will report how it comes out.
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Just checked out the snook website. Looks like that is a great resource. How does yours compare to what snook says. In other words, do you have a good one?
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I don't have a pair that look remotely like Keith's beautiful restorations, but when my step-up transformers reach me, I'll be ready to see how they sound, if at all. I've just ordered from pcX 22 resistors, replacing all but a 3W 180 ohms resistor in each chassis, and a bunch of good film caps and two electrolytics, and if I get any sound at all in the present "as is" state, I'll proceed to upgrade and see how much that helps. I wonder how hard, and how expensive, it would be to replace the 220-240 VAC power transformer with a 110-120 VAC one. I'd love not to have to use step-up transformers.
I also wondered if some clever Bottlehead would be able to get these amps working again in case they don't sound good even after all my efforts. And even change the power transformer if I can learn how to do that. I'd expect to pay for this service, of course. Someone on eBay is willing to repair a single Quad II for $195 plus $52 shipping back to me, and with my shipping to him, that's too expensive, and would duplicate all the component changes I'll make--so I'm hoping for a better rescue than that.
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Might be difficult to trust an Ebay contact, I'm not sure. On the other hand their are several BH's I'd definitely trust. $250 for the job really doesn't sound that bad. What about Snook?
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PJ,
Where does that screen grid cap connect? Wondering if this is the ame cap connection that Deccware calls alternatively the "Christmas Comes Early" or Hazen Grid Mod"?
-- Jim
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Jim, the phase splitter is a pair of EF86 in paraphase. Each screen is fed from a 1 meg resistor. The capacitor is between the two screens - there is no cap to ground or to the cathodes, which you might normally expect. The cathode bias resistor is also unbypassed, and the feedback goes there, i.e. shared by the two tubes.
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My step-up transformers arrived and I could finally hear what the Quad II's sounded like, with luck. I didn't have great luck: a few minutes of good-sounding music from one amp, then switched to the other and a transformer fuse blew immediately. Switching back to the first amp, it played for less than a minute before a transformer fuse blew. These are 200W transformers. My homemade) cord is fine, transformers work with nothing plugged into "240 Out", so the problem must be in the amps. All I've done is to install RCA jacks, the center (for the pin) going to Jones plug socket #2, called "Input" on the circuit diagram, where the RCA jack shell goes to ground. Resistor R1, 1M ohms, is still in place between socket #2 and ground. I can't see that I've done anything bad there, getting the RCA jack installed. My question: where should I look for the trouble that's causing the transformer fuses to blow? Not easy to answer from a distance, I realize--but with so much expertise available on this Forum, why not try?
I've ordered replacements for all resistors but the 3W 180R ones, which read close between the two chassis, and replacements for film caps C1, C2, C3 and more film caps to use as bypasses wherever I can find the two connection points for out-of-sight electrolytics. Maybe making all those changes will eliminate the blown fuse problem without my ever discovering what it was. Hope springs eternal.
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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.
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Presumably, the amps themselves were set to the "230V -250V" range you mentioned earlier?
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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?
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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"?
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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?
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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.
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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?
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Have you made progress on the Quad II's?
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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.