GSG upgrades

2nd harmonics for the masses

GSG upgrades

Postby ecir38 » Mon Jun 02, 2008 5:07 pm

Min, thought I would give you an update of your GSG 300B since it has come up a couple of times in the UX4 socket thread here http://www.diytube.com/phpBB2/viewtopic.php?t=2658.

Upgraded the solid state rectifier to include a RRFSR per ed http://diytube.com/phpBB2/viewtopic.php?t=2280, changed the tubes to Sophia Electric Princess 300B mesh plates, and swapped the coupling caps to .22uf K40Y-9's. All of these were done about a month or so apart with each of them making a worthwhile improvement.

Swapping the tubes from the Electro Harmonix made this amp allot more laid back and the the K40Y-9's brought it back up to speed.

I think I will play with bypassing the cathode bypass caps with solen fast caps next.
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Postby SDS-PAGE » Mon Jun 02, 2008 8:25 pm

Thanks for the update. You did just the right things to upgrade your amp - rolling tubes and upgrading caps. I tend to think the former has a greater effect, but the latter can be as important as I found out with my 2A3 amp. You also did a smart thing in isolating each improvement.

Sophia electric 300Bs must have cost you some dough, eh? I am using JJs 50W 300Bs that I got for $210/pr and I am pretty happy with it. I got those EHs for $110/pr when I built yours. I see that the price has gone up by at least 40 bucks since then on eBay. Just curious, have you played with different 6SL7s? -Min
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Postby ecir38 » Mon Jun 02, 2008 9:24 pm

Actually I got the Sophia's on Audiogon for under 200 shipped with a little over 100 hrs. They test good for the price I got them.

For the 6SL7 varient I settled on the Sylvania VT-229. I would like to try the Mullard ECC35 or a Tung Sol 6SU7 GTY but haven't found a good enough deal on them yet.

The biggest change was the Electro Harmonix tube, it just didn't do this amp justice. I wasn't really crazy about the Sophia's until I installed the K40Y-9's they were just too laid back and now see why people are raving about the K40Y-9.

The nice thing about about DIY amps is you can play with them to get the sound you are looking for. I do think I got lucky with the combination above, maybe I will throw the Electro Harmonix back in to see if I like the differance the K40Y-9's make to them.

One note is that I had to relocate R7, R8 and R11, R12 to the top side of the board to allow clearance for the K40Y-9's.
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