cheersI have it from an extensive article from Vacuum Tube Valley that the 6L6 was introduced in March 1936. It is not clear when the 807 followed; it appears that the 807 different base may have been so that it could be conveniently substituted for other similar tubes. The 6BG6G (as a repackaged 6L6) came out in 1946.
Rereading these articles, I have another worry, which I am too stupid to sort out, and that is with the box-shaped anodes of the Russian versions. These compared to the original oval shape. As I can gather (and which sounds logical), the "virtual cathode" effect of the cloud of electrons near the anode (acting as a replacement for a suppressor grid) requires a rather critical position of anode for most efficient operation. That is also why there are beam electrodes, to limit electron flow to the correct part of the anode. In a flat anode the central part is rather closer to the screen etc. than the extremities still in the beam path. What is the effect of this? Some seem to think it is important, but then again the KT66 had a "flat" anode from the beginning.
While I am at it, I have just received 10 6L6EHs. I originally liked the looks, but now find that the structure, while mounted on pins direct from the base, is sometimes only connected to the pins by flimsy strips of metal as before. Part of the higher dissipation of the 6L6GC comes from slight extra cooling through the base pins - this is evident in NOS GEs where everything is directly spot-welded to rather thick leads to outside.
After all that then, can anybody verify that a 6L6EH is in fact equivalent to the 6L6GC (Pa = 30W), or do we have to do with more approximations by the Russians? (This may sound quite academic to some, but small differences can impact on tube reliability.)
Tubelab (among others): Any guidance here?
Thanks and regards.
Rereading these articles, I have another worry, which I am too stupid to sort out, and that is with the box-shaped anodes of the Russian versions. These compared to the original oval shape. As I can gather (and which sounds logical), the "virtual cathode" effect of the cloud of electrons near the anode (acting as a replacement for a suppressor grid) requires a rather critical position of anode for most efficient operation. That is also why there are beam electrodes, to limit electron flow to the correct part of the anode. In a flat anode the central part is rather closer to the screen etc. than the extremities still in the beam path. What is the effect of this? Some seem to think it is important, but then again the KT66 had a "flat" anode from the beginning.
While I am at it, I have just received 10 6L6EHs. I originally liked the looks, but now find that the structure, while mounted on pins direct from the base, is sometimes only connected to the pins by flimsy strips of metal as before. Part of the higher dissipation of the 6L6GC comes from slight extra cooling through the base pins - this is evident in NOS GEs where everything is directly spot-welded to rather thick leads to outside.
After all that then, can anybody verify that a 6L6EH is in fact equivalent to the 6L6GC (Pa = 30W), or do we have to do with more approximations by the Russians? (This may sound quite academic to some, but small differences can impact on tube reliability.)
Tubelab (among others): Any guidance here?
Thanks and regards.
Turbo7MN,
Replacement of 8417s with 6BG6s (6L6 topology) is quite a step. You may know that the gm of the 8417 is a very high 23000 u.mhos compared to the 6L6 modest gm of about 5200 u.mho. I do not have inter-electrode capacitances for the 8417, but judging from the structural differences I would imagine that they will differ. You have already read that bias for the 6BG6 will have to be some 2,5 times higher.
I am also just thinking that you may be stressing the 6BG6; my RCA book gives its Pa as only 20W compared to 35W for the 8417 (that is one vicious tube!). Within that limit you will be hard put to get 60W back, although the available anode voltage swing can be much higher (but then you will require a different output transformer primary impedance). You would also need more gain to drive them, apart from perhaps having to re-assess feedback stability if you have feedback.
Sorry if I am giving information you already know, but just to be safe.
Regards.
Replacement of 8417s with 6BG6s (6L6 topology) is quite a step. You may know that the gm of the 8417 is a very high 23000 u.mhos compared to the 6L6 modest gm of about 5200 u.mho. I do not have inter-electrode capacitances for the 8417, but judging from the structural differences I would imagine that they will differ. You have already read that bias for the 6BG6 will have to be some 2,5 times higher.
I am also just thinking that you may be stressing the 6BG6; my RCA book gives its Pa as only 20W compared to 35W for the 8417 (that is one vicious tube!). Within that limit you will be hard put to get 60W back, although the available anode voltage swing can be much higher (but then you will require a different output transformer primary impedance). You would also need more gain to drive them, apart from perhaps having to re-assess feedback stability if you have feedback.
Sorry if I am giving information you already know, but just to be safe.
Regards.
I have only limited experience with Russian 6L6 types. Several years ago I bought some Russian tubes cheap on Ebay from a guy in Hong Kong. The 6L6 types were branded "Orion". I put 2 of them in a 50 watt guitar amp several years ago. They are still going strong. I use the other 4 for testing out new designs before using good tubes. They have taken a beating without failure. On the other hand I got a bunch of Orion EL-34's and they all blew up.
I have tried Svetlana (the real ones) with good luck, but I have not tried any of the Reflector sourced tubes.
As far as the plate shape is concerned, I am not sure if the boxed plate structure is a bad thing. Yes this puts the center of the plate area closer to the cathode, and this area is the first to glow when you abuse it. It is also where the heat radiating fins are attached. In my abuse testing of sweep tubes, the ones that have the boxed plates seem to do better than the ones with rounded plates. (Tubes with the same type number)
As far as which came first 807 or 6L6 I don't know, but it is obvious that they both come from the same mold. I found several broken ones of both types, which I dissected. Tubes from the same manufacturer have the same guts. As previously the 6BG6 came later. It was made for TV sweep tube use. The old ones that I found have the same guts as the 807 and 6L6GB. These are all old surplus dating back to WWII.
I have tried Svetlana (the real ones) with good luck, but I have not tried any of the Reflector sourced tubes.
As far as the plate shape is concerned, I am not sure if the boxed plate structure is a bad thing. Yes this puts the center of the plate area closer to the cathode, and this area is the first to glow when you abuse it. It is also where the heat radiating fins are attached. In my abuse testing of sweep tubes, the ones that have the boxed plates seem to do better than the ones with rounded plates. (Tubes with the same type number)
As far as which came first 807 or 6L6 I don't know, but it is obvious that they both come from the same mold. I found several broken ones of both types, which I dissected. Tubes from the same manufacturer have the same guts. As previously the 6BG6 came later. It was made for TV sweep tube use. The old ones that I found have the same guts as the 807 and 6L6GB. These are all old surplus dating back to WWII.
Hi Johan,
I've used many 6L6EH tubes (right from New Sensor). They are some of the very few that Fender Twins don't eat, Fender does push the plate B+ rating. They also survived Mesa Barons. These will eat Svetlana's some times, and EL34's almost always.
I am very confident about the quality of these tubes. Also, the last place you want heat to flow is into the socket. That will ruin the tension of the pins.
You can't group these in with "Russian" tubes. Sovteks burnt right away in some Fenders. I didn't get any that didn't at least hum or turn a little red. They are built in Russia, but to a higher quality.
-Chris (oh, Good Morning!)
I've used many 6L6EH tubes (right from New Sensor). They are some of the very few that Fender Twins don't eat, Fender does push the plate B+ rating. They also survived Mesa Barons. These will eat Svetlana's some times, and EL34's almost always.
I am very confident about the quality of these tubes. Also, the last place you want heat to flow is into the socket. That will ruin the tension of the pins.
You can't group these in with "Russian" tubes. Sovteks burnt right away in some Fenders. I didn't get any that didn't at least hum or turn a little red. They are built in Russia, but to a higher quality.
-Chris (oh, Good Morning!)
Well,
I have a GE brand 6BG6GA rigged into my Fender Champ now. BUT, Looks like I still have a bit of tinkering ahead.
Some who remember my early fender champ thread may remember this one. But, I will say It sounds very Ummmmmm interesting so far. Has a lot of chime like a 6V6GTA , The Bottom end is fair considering my OPT is rather small.
It is a cleaner sounding tube than the 6L6GC I had in the amp, But it had a load of miles on it.
I am clearly running hot,
Not hot enough to red plate, But hotter than expected or desired.
I figured its just sitting there collecting dust, If I am going to melt one down, This is the perfect choice!
So I am inspired to tinker with it a bit more.
I have always had this problem with this particular amp. Though built basically identical to a couple others I built back then, I have a cut-off issue that I never found the source of. Only with Full treble and volume settings, I back off the treble to 75% its fine.
I thought It was A PT issue until I found a good replacement last weekend.
SO, all I can say is, I for sure get as much power as the 6L6GC I had in the unit, (which was also hot).
Its a darn loud 5 Watter.
I am betting in a good amp it would easily be a great alternative.
Trout
I have a GE brand 6BG6GA rigged into my Fender Champ now. BUT, Looks like I still have a bit of tinkering ahead.
Some who remember my early fender champ thread may remember this one. But, I will say It sounds very Ummmmmm interesting so far. Has a lot of chime like a 6V6GTA , The Bottom end is fair considering my OPT is rather small.
It is a cleaner sounding tube than the 6L6GC I had in the amp, But it had a load of miles on it.
I am clearly running hot,
Not hot enough to red plate, But hotter than expected or desired.
I figured its just sitting there collecting dust, If I am going to melt one down, This is the perfect choice!
So I am inspired to tinker with it a bit more.
I have always had this problem with this particular amp. Though built basically identical to a couple others I built back then, I have a cut-off issue that I never found the source of. Only with Full treble and volume settings, I back off the treble to 75% its fine.
I thought It was A PT issue until I found a good replacement last weekend.
SO, all I can say is, I for sure get as much power as the 6L6GC I had in the unit, (which was also hot).
Its a darn loud 5 Watter.
I am betting in a good amp it would easily be a great alternative.
Trout
anatech said:
ha-ha Chris,
Its not so much the bad 6L6 in that
Champ,I beleive its an evil spirit living in the chassis
I think I have used 1/2 lb of solder rebuilding that thing 7 times. Trust me, Its haunted with the evil spirits of 1920's tube engineers that resent rock N roll!
Im gonna get the voltage lists off of it tomorrow, I need to finish up on a faceplate design yet today.
Gene
Trust me, anyone who has built a few amps has built something that was possessed! Most of my disasters were solid state. Thet blew up violently. I rebuilt them, and they blew up again. After a few trips to the parts store only to generate more smoke, I threw the whole thing out. This happend enough times for me to give up amp building for several years in the late 70's.
Trout:
In one of your future Champ type designs try the $18 Edcor transformer. It will blow away the Triode $14 transformer. See this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72654&highlight=
It has a UL tap which opens up a new world of sounds and more power too.
Trout:
In one of your future Champ type designs try the $18 Edcor transformer. It will blow away the Triode $14 transformer. See this thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72654&highlight=
It has a UL tap which opens up a new world of sounds and more power too.
Those Look Great.
I had only 1 of those triode OPTs left so I will switch to the Edcors, In all honesty, I have always had doubts about the ones I had. When 2 out of 5 units which were otherwise identical gave me problems, I began to question quality control or tolerances. I have not been able to get the last one to work right and doubt it ever will.
The Price differences are minimal and I plan on ordering a few .
Trout
anatech said:
No, sure, on a large scale. But I did read that that bit of extra heat conduction, plus a larger radiator on G1 was the main reason for being able to take the dissipation of the original structure from 19W to 30W. Then one has the 7027 (which I have never seen!)at 35W. I sometimes wonder how relative these ratings are. (From tubes I dissected I did not notice anything else like change in metal gauges, etc. to indicate that more heat can be tolerated.)
Excuse my ignorance, but when you mention that Fenders etc. eat tubes, what exactly is the stressing factor: high current, high voltage, insufficient air flow? Under what conditions do they work?
Regards.
Hi Johan,
Fender sticks them upside down. Plate voltage varies between 460 and 475 VDC. Higher if your AC is high. I imagine the output transformer gets saturated during regular loud play as well.
These amps are a great test of the quality of tube. Even the ECG/Sylvania 6L6GC's don't cut it in these. I was using 7581A/KT-66 Jan tubes as these were the only ones I could rely on. I was surprised when I tried the 6L6EH in there. I honestly expected at least excessive hum.
If a brand of 6L6GC will run well in a Fender Twin - it has my respect.
-Chris
Fender sticks them upside down. Plate voltage varies between 460 and 475 VDC. Higher if your AC is high. I imagine the output transformer gets saturated during regular loud play as well.
These amps are a great test of the quality of tube. Even the ECG/Sylvania 6L6GC's don't cut it in these. I was using 7581A/KT-66 Jan tubes as these were the only ones I could rely on. I was surprised when I tried the 6L6EH in there. I honestly expected at least excessive hum.
If a brand of 6L6GC will run well in a Fender Twin - it has my respect.
-Chris
I want to echo and agree with Anatech's observations. First, Fender hangs the tubes upside down. The heat rises, right into the tubes base, cooking the life out of the glue, and the base itself, and causing the heat to be trapped in the tube. Second, the old Fenders often operate the tubes at or above the maximum ratings. Third, watt for watt, a Fender has the physically smallest output transformer of the major guitar amps. This leads to transformer saturation. This is partially responsible for the Fender sound (when cranked to 10), but when the transformer saturates, the tube current soars, and bad things begin to happen.
Some of the old Fenders had a rear panel that trapped the heat inside the box (my old Bandmaster) by restricting airflow.
Then think about how the average guitar amp gets used. The input is often overdriven, the amp is often operated with the wrong speaker impedance, and the amp is operated well into clipping for hours at a time. The amp is either sitting on top of the speaker cabinet, or inside it. The tubes get a constant shaking, especially with a bass guitar amp. All guitar amps eat tubes more often than a typical HiFi amp, but certain ones have a reputation for being hungry. Wimpy tubes need not apply!
Thanks all!
Yes, I can now recall having seen what has been described. Terrible! Valuable information, in times when guarantees no longer necessarily reside in the make.
As perhaps mentioned (I did not look back), I use the 6L6s at Va = 560V and Vg2 = 460V; Ia = 50 mA each. I hope I will not need to reply back that that caused trouble.
Regards.
Yes, I can now recall having seen what has been described. Terrible! Valuable information, in times when guarantees no longer necessarily reside in the make.
As perhaps mentioned (I did not look back), I use the 6L6s at Va = 560V and Vg2 = 460V; Ia = 50 mA each. I hope I will not need to reply back that that caused trouble.
Regards.
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