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Old 2nd September 2008, 02:13 PM   #11
SY is offline SY  United States
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Do you know the plate to plate impedance of the Quicksilver output transformer? Though the "6BG6" will work fine with 4500-5000 ohm, a bit higher is better. The best I've tried so far was a 500 volt rail and 6600 ohms.

The difficulty for a direct drop-in is that the "6BG6" has a higher drive voltage requirement. You'll have to modify the bias supply to get a higher voltage and ensure that the driver stage is capable of the extra swing. That said, it will end up being a much more rugged and reliable amp.
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Old 2nd September 2008, 05:34 PM   #12
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Thanks for the information. I don't readily have the answers to your questions.

The reason I also asked burnedfingers to respond is because he stated he already had a Quicksilver 8417 converted amp, and could possibly run through the exact changes he made. That would be a plus.

Also, not stated earlier, I have some of the SND 6BG6GA tubes just gathering dust . I was able to snag a box of 100 several years ago when he was willing to let them go for cheap, about $3.25 per tube at that quantity as I recall. So I've been looking for places to use these other than as just replacements for my standard 6L6 stuff.
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Old 3rd September 2008, 01:28 AM   #13
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I sent you an email Ohighway.

First try them in your Stereo 70 and you will be amazed at the difference. If your a convert then we will do the Quicksilver mod.

Convert your stereo 70 to individual tube bias first and then change the first 10K resistor in the bias circuit to 6.7Kor so and see if they will all bias up correctly. If they do then enjoy and if not go to a slightly smaller bias resistor and bias it again. I put a switch in so I could used the stock bias resistor for the EL34's.

You will need the conversion tube bases or you will have to rewire the output tube sockets for the 6BG6GA's. I purchased the bases and this way I can pop the EL34's back in if I desire.

I think the stereo 70 is 4200 or 4300 ohm output transformers and so is the Quicksilver.

My personal opinion of the EL34 Quicksilver mod is that it doesn't cut it. I assume part of the problem might be the modifications to the front end.
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Old 3rd September 2008, 06:36 AM   #14
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Thanks for the information. I have a scrappy looking stereo 70 that needs a rebuild anyway, so I'll likely use that as a testbed.

Though I haven't personally heard it, I recently talked with an original 8417 Quicksilver owner who had Quicksilver perform the EL34 conversion. His take on it...... "the magic was gone".

My audiophile type friends hold the EL34 in very high esteem, however I don't personally worship at that altar. I tend to prefer the sound of tubes like the 6L6, 7591, and even the 6V6. They have a cleaner more crisp sound than the EL34 ( or EL84 for that matter).
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