J,
What amp did you have in mind?
I can't seem to find a reference to a specific amp from your previous posts here?
Sorry about that sick sense of humour of mine.😉
What amp did you have in mind?
I can't seem to find a reference to a specific amp from your previous posts here?
Sorry about that sick sense of humour of mine.😉
Re: Re: KT77 or EL34
Or in my case the - EF86, 12AX7, EL34 (or KT77) class AB1 PP ultra linear version with new Hammond 5k OPT and all new resistors and caps with better PSU regulation/filtering and better bias controls and improved sensitivity also less caps in signal path.
Claus Byrith mods:
http://www.lundahl.se/claus_b.html
Le Basseur said:
Or in my case the - EF86, 12AX7, EL34 (or KT77) class AB1 PP ultra linear version with new Hammond 5k OPT and all new resistors and caps with better PSU regulation/filtering and better bias controls and improved sensitivity also less caps in signal path.
Claus Byrith mods:
http://www.lundahl.se/claus_b.html
Investing On A Budget....
Hi,
Personally, I would follow EC8010s' advice...if you can afford it.
With the profits of that you could allow yourself a number of KT77s for yourself to check on the Mullard amp and still invest in some other stuff your source is willing to let go.
That's just to show how tube crazy I can get.😉
Hi,
Personally, I would follow EC8010s' advice...if you can afford it.
With the profits of that you could allow yourself a number of KT77s for yourself to check on the Mullard amp and still invest in some other stuff your source is willing to let go.
That's just to show how tube crazy I can get.😉
Re: Investing On A Budget....
Bussy becoming like that myself , those damn crazy - vacuum , tube, valve, hollow, glass things
Thanx for good discussions and g'night !!
fdegrove said:
Bussy becoming like that myself , those damn crazy - vacuum , tube, valve, hollow, glass things
Thanx for good discussions and g'night !!
I'll study the modified schematic from the link you posted,and,if you agree,I'll make my comments (if really needed).
See ya! (...so to speak....)
See ya! (...so to speak....)
KT77 compared with EL34 (and other tubes)
Hi,
A reply much too late to be of use in addressing your specific question, I suspect, but I thought I would just post my thoughts/findings on this for general interest and info.
First of all, note that whilst the KT77 and EL34 are similar, they are NOT (contrary to much stuff posted on the Web) completely equivalent.
For starters, one is a beam tetrode (the KT77) whilst the EL34 is strictly a pentode. Not that much difference between the properties of these two fundamental power tube types, I know, but they still are NOT the same.
Secondly, be careful in that the pin-outs also are not identical. Again, lots of postings on the Web suggest that the KT77 and EL34 are "drop-in" replacements for one another, but be aware the pin 1 connection is not the same. The EL34 uses pin 1 for its suppressor grid connection (g3), which is usually connected to the cathode externally. The KT77 makes NO connection to pin 1, and the connection between the beam-plates and cathode is made internally .
This means that it's usually safe to sub a KT77 in place of the EL34 (as is sometimes recommended as an "upgrade"), but do take care doing the reverse - that is, if trying to use an EL34 to replace the KT77. Amps designed around the KT77 may not necessarily ground pin 1 of the socket, and indeed some use this pin as a spare tag. My Grant-Lumley GL50A amp uses this pin as an anchor point for a 33 ohm stopper resistor in series with the sceen grid, so dropping an EL34 into the socket ties the suppressor grid to the screen grid (more or less)!
Finally, the maximum anode dissipation of the EL34 is a bit less at 25 W compared with 32 W for the KT77 (although in fairness for decent life the M-O Valve Co recommended derating to 25 W total anode + screen).
I tried to replace the more-or-less unobtainable M-O KT77's in my Grant GL50A with EL34's; this is how I found out about the pin 1 issue. However, even with pin 1 properly returned to cathode, the EL34 sounded frankly lousy in this amp, really thin and harsh, and lacking in power. I ended up replacing the '77s with KT88's (yes, I know the heaters draw more current but the mains tranny is OK with this) and then re-biasing. This was a MUCH better result, the 88's sounding actually much better even than the original KT77's. This substitution brought up another point in the "pin 1" department, in that both the KT88 and 6550 connect the metallization around the base to pin 1, and again if your KT77 amp - like mine - uses pin 1 for a circuit connection, the metal gets connected to this. In my case the result was a literally a shock, because metal round the tube bases was "live" at screen potential of over 400 V - ouch! 😱
Regarding amps designed with the EL34, such as the Mullard 5-20 and Radford STA series, I guess the KT77 would be a fine substitute, should last longer and might well be a worthwhile sonic upgrade. However, these amps were designed around the EL34 and so should (unlike my Grant) work fine with their original tube type.
Mike
Hi,
A reply much too late to be of use in addressing your specific question, I suspect, but I thought I would just post my thoughts/findings on this for general interest and info.
First of all, note that whilst the KT77 and EL34 are similar, they are NOT (contrary to much stuff posted on the Web) completely equivalent.
For starters, one is a beam tetrode (the KT77) whilst the EL34 is strictly a pentode. Not that much difference between the properties of these two fundamental power tube types, I know, but they still are NOT the same.
Secondly, be careful in that the pin-outs also are not identical. Again, lots of postings on the Web suggest that the KT77 and EL34 are "drop-in" replacements for one another, but be aware the pin 1 connection is not the same. The EL34 uses pin 1 for its suppressor grid connection (g3), which is usually connected to the cathode externally. The KT77 makes NO connection to pin 1, and the connection between the beam-plates and cathode is made internally .
This means that it's usually safe to sub a KT77 in place of the EL34 (as is sometimes recommended as an "upgrade"), but do take care doing the reverse - that is, if trying to use an EL34 to replace the KT77. Amps designed around the KT77 may not necessarily ground pin 1 of the socket, and indeed some use this pin as a spare tag. My Grant-Lumley GL50A amp uses this pin as an anchor point for a 33 ohm stopper resistor in series with the sceen grid, so dropping an EL34 into the socket ties the suppressor grid to the screen grid (more or less)!
Finally, the maximum anode dissipation of the EL34 is a bit less at 25 W compared with 32 W for the KT77 (although in fairness for decent life the M-O Valve Co recommended derating to 25 W total anode + screen).
I tried to replace the more-or-less unobtainable M-O KT77's in my Grant GL50A with EL34's; this is how I found out about the pin 1 issue. However, even with pin 1 properly returned to cathode, the EL34 sounded frankly lousy in this amp, really thin and harsh, and lacking in power. I ended up replacing the '77s with KT88's (yes, I know the heaters draw more current but the mains tranny is OK with this) and then re-biasing. This was a MUCH better result, the 88's sounding actually much better even than the original KT77's. This substitution brought up another point in the "pin 1" department, in that both the KT88 and 6550 connect the metallization around the base to pin 1, and again if your KT77 amp - like mine - uses pin 1 for a circuit connection, the metal gets connected to this. In my case the result was a literally a shock, because metal round the tube bases was "live" at screen potential of over 400 V - ouch! 😱
Regarding amps designed with the EL34, such as the Mullard 5-20 and Radford STA series, I guess the KT77 would be a fine substitute, should last longer and might well be a worthwhile sonic upgrade. However, these amps were designed around the EL34 and so should (unlike my Grant) work fine with their original tube type.
Mike
Hi,
Thank you for your comments, Mike.
In all fairness 🙂 not all the 6550s have a hardwired connection from pin#1 to their metal collar.
Apparently this is the case with current production Svetlana 6550s, maybe some others as well.
Not sure what the situation is with KT88s nowadays but better safe then sorry I'd say.
Cheers,😉
Thank you for your comments, Mike.
In all fairness 🙂 not all the 6550s have a hardwired connection from pin#1 to their metal collar.
Apparently this is the case with current production Svetlana 6550s, maybe some others as well.
Not sure what the situation is with KT88s nowadays but better safe then sorry I'd say.
Cheers,😉
6CA7EH sounds good
Hi All,
I rebuilt an Eico HF-87a a while back. I was careful to return it to spec. Darn thing sounds great. I did change the El-34's with Sovteks. That improved things, then with ElectroHarmonix 6CA7's. That gave a vast improvement in sound quality. I have since changed all tubes to ElectroHarmonix one at a time. Man, the 12AX7EH is quiet. In general, I like that brand and they are tough. 6L6EH's are good too.
They are not expensive, give the 6CA7EH's a try. Comments?
-Chris
Hi All,
I rebuilt an Eico HF-87a a while back. I was careful to return it to spec. Darn thing sounds great. I did change the El-34's with Sovteks. That improved things, then with ElectroHarmonix 6CA7's. That gave a vast improvement in sound quality. I have since changed all tubes to ElectroHarmonix one at a time. Man, the 12AX7EH is quiet. In general, I like that brand and they are tough. 6L6EH's are good too.
They are not expensive, give the 6CA7EH's a try. Comments?
-Chris
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