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Hi
I am getting confused. I got a pair of Fisher monoblocks model 100. On the chassis is written EL37 as output tubes. It happens to have a quad of KT66. Are all of the above EL37/KT66/6L6CG compatible with no other complications ??
thank you
Follow Ups:
I think you will find minor differences between the three, or they would bear the same nomenclature...The important difference is in plate dissipation (max) figures. Also, the KT-66 was originally characterized as being useful in the power grid region (over 0V grid)in a limited duty cycle, as some 6L6 specs. They all have max plate voltage ratings which differ slightly, and if you compare the plate curves I am sure you will find some minor differences. Generally, they are interchangeable, having basically the same heater ratings, as long as you do not use an EL-37 where a KT-66 is specified (it has the highest ratings of the three for Vp max, Pd max). The 6L6 and KT-66 can both be used in any application where an EL-37 is specified. Where a KT-66 is specified, as in some Williamson designs with high B+, I would be hesitant to use an EL-37 and some 6L6, like the "G" version.
Hope this helps.
S
My SE40 uses 5881/6L6GC and I have measured the plate voltage to be 472V, will there be any problem in using KT66 instead of the 5881/6L6GC ?Thanks
Since the KT-66 has the highest max. plate Voltage rating of the three, it could be used at a higher B+ than the other types; (...the 5881 has a rating in the GE manual(15L)of 360 max volts while others show it "same as 6L6GC", so there may be some differences brand to brand.) The heater current of the KT-66 IS higher than the 6L6 types (I still think the EL-37 is less than 1A)so some heater supplies may be insufficient for its use, but with respect to plate volts, in your application it is not an issue.
SA
Correct me if I am wrong, but I thought the EL37 has the highest plate voltage and plate dissipation of the 6L6 family (except the Bendix 6384, which has an instantaneous plate rating of 1500V!). The EL37 can take almost 800V on its plate and dissipates 30W. The filament current is 1.4A as opposed to 1.27A for the KT66.
There are few amps designed to take advantage of the ratings of the EL37. However, some amps such as the Leak TL25+ states that KT66, EL34 or 5881 can be used. In reality, even a GEC KT66 will not survive long in these amps, but an EL37 would do very nicely, thank you.
Seems to me that the 5881 has the lowest plate V rating of the whole bunch according to RCA and GE data, so I do not know how the Leak could specify it when a KT-66 will not survive. Since the common ratings for the EL-34 are 30W (32 in TR) and 800V, how is that inferior to the EL-37 in those respects? Re the heater currents, after seeing so many differing opinions I measured the KT-66 (genalex) this morning and got 1.34A @ 6.30V, so I was low, and Koo was closer. As I said to Koo, I want to see some hard data on the EL-37, because my experience with them is dated, and I want to know how they can pull off those ratings with such a small plate. If you have some maunfacturer specs, PLEASE show me because I really want to get to the bottom of this,
Thank you very much.
SA
EL34 is not in the 6L6 family, so it doesn't count. The TL25+ can use tubes of different families because of the "automatic bias" design. The experience of vintage amp collectors is such that KT66 don't last long in this amp, unless you lower the HT, but EL37 would do fine. Nobody is stupid enough to put a 5881 in, but a 6L6GC would probably do better.
According to VTV issue 4 #1, EL37 has a plate dissipation of 25W and a plate and screen voltage of 800V. KT66 has a plate dissipation of 25W, plate voltage of 500V and screen voltage of 400V. The 5881 has a plate voltage of 360V and screen voltage of 270V. The 6L6GC is similar to the KT66.
A triode wired KT66 with 300V on the plate has a distortion of 0.63%, and the EL37 has 0.78%. Pentode wired KT66 with 500V on the plate and 300V on the screen has 0.88% distortion and the EL37 has 0.91%.
I have both the clear and smoke glass KT66, and three different quads of clear glass tall bottle EL37. I actually slightly prefer the sound of the EL37.
thanks for the info
What I really wanted was actual complete manufacturers data re the EL-37, and not just Pd and max V. Data for the others (except the genalex KT-66) is available in abundance. The VTV data re distortions is not too pertinent for individual tube characteristics without knowing the plate load resistance for the test, and the plate resistances of the different tubes at the operating point used for the test. I think unless the tubes have identical plate resistance under those conditions, they will all measure differently for a fixed value of loading. The only curves I have for the EL-37 is ouput power and 2nd and 3d harmonics versus plate loading resistance, and I really am not interested in substitution compatibility.
Thanks
SA
nt
I sure would like to see some complete data on the EL-37 if you can recommend a good source..I was going by the measurements I took years ago when I had a pair (Mullards I think)but they are long gone...BTW whats your take on the relationship between max plate pwr vs. heater power on these; it would appear that they do not follow the norm
Thanks
SA
Oops..I meant heater power to plate current max relationship
Thanks
SA
The heater current and max. plate voltage are the essential electrical parameters to be looked into for tube substitution. There are no direct relationship. The same principle applies to other tubes sub. such as GZ34, 5U4.
The link for duncansmps is:http://www.duncanamps.com/
I was not referring to any "substitution" data. I meant heater power vs plate current as I said, hoping you knew something slightly non-typical re: the EL-37 and its particular design rationale. Yes there is a relationship.
Anode
Sorry, my misunderstanding. When I put those parameters together, there was no direct relationship in the context or better say, in my mind. Really, there should be..in the real world due to ionization. But I couldn't find any clue.Your user name reminds me a relationship with cathodic protection of water pipes.
It is a very old corporate product development metaphoric reference
In general, a tube can be safely substituted by one with higher plate current and lower filament current, electrically. The data of 6L6GC/EL37/KT66 are as follows:-(Max plate voltage/filament current)
400V/0.9A
400V/1.4A
600V/1.4A
Whether you wish to add extra filament transformer when changing from 6L6GC to KT66 or EL37, your own choice. Someone suggested that a CRO could check the overloading but I would say the temperature rise test of the PT filament output would govern how much current you can draw, without exceeding the design limit. Such heat run test is valid for all electrical equipment and the temperature can be measured by change of resistance method or RTD(resistance temperature detector)embedded inside the winding(for large machine or transformer, of course)The data sheet usually indicated the anode to cathode voltage whilst the schematic usually represented the voltage to ground. So, don't mix them up. In this case, KT66 can be safely used with respect to plate voltage.
nt
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