I'm in total agreement with Chris's remarks. 6550/KT88 sort of stuff is a much more appropriate replacement. An interesting possible dark horse (it will take some clever mechanics and a rework of the power supply) is a triplet of EL84.
The 8417 was always a twitchy, unreliable, and inconsistent tube- with its unusually high sensitivity, how could it be otherwise? Like a classic Triumph, they were fine when they worked, but they didn't always work.
The 8417 was always a twitchy, unreliable, and inconsistent tube- with its unusually high sensitivity, how could it be otherwise? Like a classic Triumph, they were fine when they worked, but they didn't always work.
You know, if I did'nt know better I would take offence.
"Classic Triumph" Is there any other Triumph?
"when they worked" they always worked when they started!
"they didn't always work" OOOohhhh please. They always worked when they wanted to!
Its a wonder you didn't type something like "they leaked oil like a sieve" .
I also notice you not mentioning BSA, Hmmm. I guess you are partial to those
Happy Friday
Andrew
Hi Andrew,
Actually, I was tempted to respond that they rusted very quickly here in southren Ontario. And they really did. Positive ground + salt + water = no car. Many ex-Triumphs over here.
Beside a Harley motorcycle, nothing anyone could produce would leak oil like a sieve! Many Harleys in California. That's why no one notices!
-Chris
Actually, I was tempted to respond that they rusted very quickly here in southren Ontario. And they really did. Positive ground + salt + water = no car. Many ex-Triumphs over here.
Beside a Harley motorcycle, nothing anyone could produce would leak oil like a sieve! Many Harleys in California. That's why no one notices!
-Chris
okay, I am now back on topic.
I found this a couple months ago and being at the office could not remember where but now that I am at home I found the print out, googled it and found the cache of it here. Makes fun reading.
http://64.233.161.104/search?q=cach...how+some+products+ever+made"&hl=en&lr=lang_en
http://www.diybanter.com/q-t_37738-Re-Bogen-amp-8417-tubes-blow-up-want-my-6550-mo-100s.html]here[/URL]
I found this a couple months ago and being at the office could not remember where but now that I am at home I found the print out, googled it and found the cache of it here. Makes fun reading.
http://64.233.161.104/search?q=cach...how+some+products+ever+made"&hl=en&lr=lang_en
http://www.diybanter.com/q-t_37738-Re-Bogen-amp-8417-tubes-blow-up-want-my-6550-mo-100s.html]here[/URL]
After reading this on the "Quicksilver" site it prompted my question.
For $250/pair (plus cost of new tubes), we can modify your amplifers to use EL34 output tubes by changing the front end circuitry and the bias circuitry. We also replace the 12BH7 with a 6922.
Thanks for the input and I will leave my amps as they are.
For $250/pair (plus cost of new tubes), we can modify your amplifers to use EL34 output tubes by changing the front end circuitry and the bias circuitry. We also replace the 12BH7 with a 6922.
Thanks for the input and I will leave my amps as they are.
BSA versus 8417
> I also notice you not mentioning BSA, Hmmm.
When my BSA 250 started (how many ways can Lucas let you down?), it ran like a good lawnmower (except with large overhead valves). No comparison at all to 8417, which always started but didn't mind blowing itself up. Think of a blown nitro dragster engine, but built cheap, with a sticky throttle.
I gather that BSA made a variety of 250s over the decades, and several larger machines; no experience with their self-destructive tendencies.
The quibble between pentode and beam-power is moot. That's a 1930s patent distinction. In the end, both types evolved toward each other. The EL34 tends to have a softer knee than the others, which gives a different crunch in overdriven guitar work. In hi-fi, you should not be pushing that hard (and you really should not push 8417s into overdrive: they will take off).
In speech/music AB service, 35W or 42W is a small detail. You'll set bias somewhat below whatever plate rating you use, and dissipation will not rise on unclipped speech/music signal. A quad of any of these tubes will make as much power as you could ask in a home amp. If they don't, you need to be looking to transmitter tubes and dedicated power circuits.
And guitarists have proven, through abuse, that the better EL34s are much sturdier than their ratings suggest.
I do like 6550. If I ever fire-up my quad-8417 Dyna, I'll probably rig it for those.
The best 6L6GC can also work at these powers. It is over the original ratings, but everybody (notably Fender) pushed the ratings. From the late 1970s onward, the differences among the big tubes may be more factory and era than type-number.
Since 8417 designs are all about the high sensitivity of the 8417, any re-fit should use a high-sensitivity power tube (or a radical driver re-design, which may mangle the sparkle). But I don't think any of the rugged tubes have significantly better sensitivity than the others. 7591 has high sensitivity, but is also a little fussy and can go sick on you, is rather smaller than the big tubes, and only recently came back into production (apparently as a re-gridded modern 6L6, not an exact clone of the old structure).
The EL34 (and 6L6GC) has the small advantage of less heater power. That means in very high current situations, it will come up short next to a 6550. But in most audio use, the lower total chassis heat could be very nice, even if you avoid getting that last dB of power.
6L6GC has the small advantage that it will be available for the rest of your life. EL34 probably will too, as the anti-6L6, but I'd bet on the 6L6 as the last to vanish from the face of the earth.
> I also notice you not mentioning BSA, Hmmm.
When my BSA 250 started (how many ways can Lucas let you down?), it ran like a good lawnmower (except with large overhead valves). No comparison at all to 8417, which always started but didn't mind blowing itself up. Think of a blown nitro dragster engine, but built cheap, with a sticky throttle.
I gather that BSA made a variety of 250s over the decades, and several larger machines; no experience with their self-destructive tendencies.
The quibble between pentode and beam-power is moot. That's a 1930s patent distinction. In the end, both types evolved toward each other. The EL34 tends to have a softer knee than the others, which gives a different crunch in overdriven guitar work. In hi-fi, you should not be pushing that hard (and you really should not push 8417s into overdrive: they will take off).
In speech/music AB service, 35W or 42W is a small detail. You'll set bias somewhat below whatever plate rating you use, and dissipation will not rise on unclipped speech/music signal. A quad of any of these tubes will make as much power as you could ask in a home amp. If they don't, you need to be looking to transmitter tubes and dedicated power circuits.
And guitarists have proven, through abuse, that the better EL34s are much sturdier than their ratings suggest.
I do like 6550. If I ever fire-up my quad-8417 Dyna, I'll probably rig it for those.
The best 6L6GC can also work at these powers. It is over the original ratings, but everybody (notably Fender) pushed the ratings. From the late 1970s onward, the differences among the big tubes may be more factory and era than type-number.
Since 8417 designs are all about the high sensitivity of the 8417, any re-fit should use a high-sensitivity power tube (or a radical driver re-design, which may mangle the sparkle). But I don't think any of the rugged tubes have significantly better sensitivity than the others. 7591 has high sensitivity, but is also a little fussy and can go sick on you, is rather smaller than the big tubes, and only recently came back into production (apparently as a re-gridded modern 6L6, not an exact clone of the old structure).
The EL34 (and 6L6GC) has the small advantage of less heater power. That means in very high current situations, it will come up short next to a 6550. But in most audio use, the lower total chassis heat could be very nice, even if you avoid getting that last dB of power.
6L6GC has the small advantage that it will be available for the rest of your life. EL34 probably will too, as the anti-6L6, but I'd bet on the 6L6 as the last to vanish from the face of the earth.
Hi PRR,
My comments where not complete I guess. EL34's are a 25W plate and that has me worried in this application. 25W to 35W is a big difference. I've had bad luck with EL34's lately overheating. All new manufacture of course. Baron amps seem to like to cook these to death. The better 6L6GC's work fine in this amp. I have had better luck with 6CA7's over EL34's. Again, new manufacture.
Guitar amps B+ values drop under load more than home amps do. EL34's may not put up with as much with a stiffer supply. At these powers, I like the KT88's and 6550's as you said. Less chance of watching the whole mess nuke.
In Fenders, I normally reach for 7581A's these days, or a real KT66. Other 6L6GC's tend not to last. I have had good luck with 6L6EH.
-Chris
My comments where not complete I guess. EL34's are a 25W plate and that has me worried in this application. 25W to 35W is a big difference. I've had bad luck with EL34's lately overheating. All new manufacture of course. Baron amps seem to like to cook these to death. The better 6L6GC's work fine in this amp. I have had better luck with 6CA7's over EL34's. Again, new manufacture.
Guitar amps B+ values drop under load more than home amps do. EL34's may not put up with as much with a stiffer supply. At these powers, I like the KT88's and 6550's as you said. Less chance of watching the whole mess nuke.
In Fenders, I normally reach for 7581A's these days, or a real KT66. Other 6L6GC's tend not to last. I have had good luck with 6L6EH.
-Chris
Picking this thread up...
...because I am in the process of converting my Quicksilver 8417s to KT88s and I have had, ummm, experiences with both Triumphs and BSAs. God bless them both, along with Felix Guattari!
Anyway, on with the thread. I am newish to this site and tube stuff so be gentle. I followed the mods ala Triode, and all is fine. However, the quad of matched Sovtek KT88s I purchased to replace the 8417s have some bias issues. One pair, rated at Ip 66/Gm 7700 reads 30 on the bias meter, when the bias pot is at zero. The other pair, rated Ip66/Gm6700 reads 50 on the bias meter. I switched them as pairs from amp to amp with the same results, so it is the tubes, or at least part of it is.
Many questions!
First - does this denote an unmatched quad?
Second, assuming these did match but the zero point was still above zero - does this indicate that the bias circuit needs further tweaking to accomodate these tubes? What might this tweak be?
I appreciate any help. Thanks, Ken.
...because I am in the process of converting my Quicksilver 8417s to KT88s and I have had, ummm, experiences with both Triumphs and BSAs. God bless them both, along with Felix Guattari!
Anyway, on with the thread. I am newish to this site and tube stuff so be gentle. I followed the mods ala Triode, and all is fine. However, the quad of matched Sovtek KT88s I purchased to replace the 8417s have some bias issues. One pair, rated at Ip 66/Gm 7700 reads 30 on the bias meter, when the bias pot is at zero. The other pair, rated Ip66/Gm6700 reads 50 on the bias meter. I switched them as pairs from amp to amp with the same results, so it is the tubes, or at least part of it is.
Many questions!
First - does this denote an unmatched quad?
Second, assuming these did match but the zero point was still above zero - does this indicate that the bias circuit needs further tweaking to accomodate these tubes? What might this tweak be?
I appreciate any help. Thanks, Ken.
Hi Ken,
Why on earth would you try the Sovtek's when the Electroharmonix are so close in price?? I have had issues with Sovtek when the B+ gets up there. Electroharmonix have been great every time so far.
I am sure there may be other brands that will hold up, but once I found these I stopped causing myself pain.
-Chris
Why on earth would you try the Sovtek's when the Electroharmonix are so close in price?? I have had issues with Sovtek when the B+ gets up there. Electroharmonix have been great every time so far.
I am sure there may be other brands that will hold up, but once I found these I stopped causing myself pain.
-Chris
First of all not to disagree with Chris but I love the Sovtek KT88's and 6550's. I never had a problem with them in my Quicksilver amps.
As for your problem with bias. I scrapped the original bias pot in favor of new in my amps because I discovered there had been an event that kept the pot from tracking correctly. As for the bias since you will be running 100-110 mA I expect for the pair you still have the ability to adjust. I had the same problem when I tried some KT90's in the amps.
I would guess the tubes aren't all that matched.
As for your problem with bias. I scrapped the original bias pot in favor of new in my amps because I discovered there had been an event that kept the pot from tracking correctly. As for the bias since you will be running 100-110 mA I expect for the pair you still have the ability to adjust. I had the same problem when I tried some KT90's in the amps.
I would guess the tubes aren't all that matched.
Hi Joe,
But fair enough!
I have used Sovteks with good effect, but I have found that when things got tough, the Electroharmonix were better. Also, the Electroharmonix sounded better when I've done direct comparisons.
I used to use Sovtek all the time because there was little alternative. So Electroharmonix had to prove themselves better to me (cynical old guy that I am).
Joe, have you tried any of these yet?
-Chris
Hey! What do you think you just did ?????
But fair enough!I have used Sovteks with good effect, but I have found that when things got tough, the Electroharmonix were better. Also, the Electroharmonix sounded better when I've done direct comparisons.
I used to use Sovtek all the time because there was little alternative. So Electroharmonix had to prove themselves better to me (cynical old guy that I am).
Joe, have you tried any of these yet?
-Chris
I might be stuck with the Sovteks, we shall see. I am returning them to have them checked for matching. I may be able to exchange...
The question is, I suspect that the KT88s still won't show zero on the meter, even if the quad is properly matched. I mean, let's say both pairs read a minimum of 30 on the bias meter. In this case, would I treat 30 as the relative zero point, and bias from there? Or can I somehow adjust the bias meter circuit until that 30 turns to zero?
Again, thanks.
The question is, I suspect that the KT88s still won't show zero on the meter, even if the quad is properly matched. I mean, let's say both pairs read a minimum of 30 on the bias meter. In this case, would I treat 30 as the relative zero point, and bias from there? Or can I somehow adjust the bias meter circuit until that 30 turns to zero?
Again, thanks.
Hi Ken,
If the Sovteks are working then you will be fine. They are reliable, so don't take my comments to mean they are bad tubes (they are not).
I normally buy mine from New Sensor. Good folks. I have had only two problems over the course of 10 years or so. Neither problems had to do with New Sensor's customer care.
-Chris
If the Sovteks are working then you will be fine. They are reliable, so don't take my comments to mean they are bad tubes (they are not).
I normally buy mine from New Sensor. Good folks. I have had only two problems over the course of 10 years or so. Neither problems had to do with New Sensor's customer care.
-Chris
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