Originally Posted by Acapella11
Hi AFB, given grid 1 is furthered through pin1, how would you physically connect pin1 to pin2 for the cathode strap and then connect pin 7 (grid 3) to the pin1 socket hole in a way that isolates those two and considering that pin1 itself is still present? Without an adapter of course.
Ahah! Now that's a good question. Short answer is: I don't know, lol. But I do have clues -hard to actually use, but ideas nonetheless.
Strapping pin 1 to pin 2 without using socket hole 1 wouldn't be too hard on tubes with fairly solid pins -pins that don't break off when bent a little- you could just bend pin 1 inwards and, I guess, solder it to pin 2 close to the glass. Ugly, cumbersome, but it should work if done correctly; tube would not go very deep in the socket though but that should be OK.
Linking pin 7 somehow to empty socket hole 1 is a different story. The best "idea" I could come up with, short of an adapter, would be -and it's a little risky- to use a broken off pin from another tube (clean, straight and good quality), add a small bend to it (to be able to take it out of of socket hole, otherwise it would get stuck in there the second you push it in), and insert it into socket hole 1 along with the usual pin 7-1 mod wire, and the tube itself -taking care to isolate each modded pin from the next modded pin.
Yeah, it's difficult, but for just for testing purposes, I'd say it's pretty doable. Anyone willing to try lol? For the record, I have found that pins on US tubes are more solid and snap off more cleanly than on UK tubes, just my 2 cents.
I can -I might actually- try it, but on the MK IV with the brass protections, it is actually harder to "get in there" with a pair of needle pliers, and manhandle a broken pin in and out of a socket hole (yes, I know you can remove the brass parts, but I don't want to, it's what makes my unit look nice lol!). Testing this mod on a socket saver -and out of the actual MK unit- first might be a better idea.
Edit: But, that wasn't even why I came here to post today, I had two other things to mention, both I almost forgot about...
First, my Telefunken EH900S. After 13h of burn-in (strapped mode), these are excellent tubes, with great but not the greatest upper end detail. They are much more forward than what I'm used to lately, and sadly seem to be -excellent but- a bit lacking in clarity below ~500 Hz, so mids and low mids sound a bit bloated; still plenty great and better than most pentodes though, the standards have shifted too much for me to keep listening to these strapped is all.
Unstrapped and with grid 3 left to float away on a lonely journey away from the 4 other grids, things got much better imo. So, yes, first conclusion here -that many people had pointed out- while the strapping technique might seem "right" and seems to almost always give more detail, it doesn't always give the best sound either, and sometimes leaving grid 3 floating actually sounds more realistic. It is the case with these tubes; I got about as much upper end detail that way, better treble extension, better and larger soundstage (nothing like my strapped 5915 though!), and thinner but better and clearer mids and bass. On the floated setting, these are very very nice tubes, but I still prefer the 5915 for their boundless and speaker-like soundstage, and overall sense over "being there"; the Tele are not exactly forward when floated, but still more forward than the 5915 -like most tubes then again. Many here would love these tubes.
Second, I got my "Made in Holland" E91H in the mail today. Here I was expecting O-getter Philips Heerlen E91H dual labeled with a UK military CV number, exactly like gibosi's Amperex E91H, but what I got is actually much more interesting.
1960 Philips-Holland-Heerlen-made E91H with a D-getter (same getter as gibosi's Amperex 6687), un-pinched glass (at least not pinched like gibosi's though maybe not quite straight either), and dual labeled... IBM! So basically, Philips E91H dual control heptodes for IBM computers; which is funny, since I had just found and ordered old-world 1950 RCA-made 6BE6/6BY6 tubes specifically designed for... IBM as well!
Anyway, I tried these strapped right away, and they sound great -unburnt-in and strapped that is, whereas reports up to here have described these as too "sweet" strapped- like a tubier and funkier 5915. More on these after 10h of burn-in tonight!
Edited by Audiofanboy - 6/27/13 at 5:00am