Is the GAT / ET5 hard on tubes?

[Myles B. Astor]

Originally Posted by turntable

Thanks, I am very temped. Upscale has them at a reasonable price - comparatively of course.

At least you know the tubes are really NOS, not the crap that people pull and try to pass off as NOS.

[Joe Appierto]

Originally Posted by Myles B. Astor

At least you know the tubes are really NOS, not the crap that people pull and try to pass off as NOS.

Point well made.

[turntable]

Originally Posted by Myles B. Astor

At least you know the tubes are really NOS, not the crap that people pull and try to pass off as NOS.

Yes, some could pass off as NOC. New old crap

[turntable]

After Upscale taking over two weeks to process my order, I received the telefunken E88CC's.

Very nice indeed. Has all the extension the stk EH's have, more open midrange, a nice tight bass and grainless.

Early days, but me thinks these are excellent and worth the premium - finger crossed they last.

[plurn]

Originally Posted by turntable

Hi Guys

Did the noise issue with the GAT get resolved - well no.

Just tonight another EH 6922 went noisy. I am now down to my last 2 cj EH 6922's.

I have gone through I think about 12.

...


BTW, Lew did tell me a while back that the plate voltage should be around 85 Volts (say + or - 5 Volts), and the cathode very close to 2.1 volts. If the voltages are right, then the tubes are operating correctly.

I do need to take my GAT to the the tech to get this measured now that I am down to my last two tubes.

cheers

I have measured voltages on my Australian market 220-240V 50/60Hz ET5. There are solder points on the tube daughter-card under the tube holder that make it easy to measure voltages.

mains voltage at time of measurement 248V 50Hz

pin 1 83.3V (plate, triode 2)
pin 3 2.028V (cathode, triode 2)
pin 5 6.57V (heater - should be 6.3V)
pin 6 83.1V (plate, triode 1)
pin 8 2.054V (cathode, triode 1)

Plate and cathode voltages look fine, but the heater voltage is a bit high. ET5 was fully warmed up at time of measurement.

If this is a problem, I might need to look into a 7DJ8 (7V or 7.3V) tube until it is resolved.

Anthony

[plurn]

For comparison, I have an online double conversion uninterruptible power supply for my computers that allows me to set the output voltage to any of 220V 225V 230V and 240V so I measured the ET5 plugged into the UPS set at 220V.

mains voltage at time of measurement 221V 50Hz

pin 1 83.5V (plate, triode 2)
pin 3 2.06V (cathode, triode 2)
pin 5 6.58V (heater - should be 6.3V)
pin 6 82.9V (plate, triode 1)
pin 8 2.086V (cathode, triode 1)

So looks very similar to when receiving 248V. I measured similar heater voltage at 230V mains. So doesn't look like the mains voltage makes any difference (confirming ronenash's comments about regulation).


Extra info. Tube manufacturers seem to specify the acceptable heater voltage range for 6922 as:

Limited values

Heater voltage, v,
not less 6.0
not more 6.6

So my ET5 is within that - just on the high side. It is about 4.4% above the nominal 6.3V which is not a huge amount. I have also read that "operation above allowable range deteriorates the very long term emission life to perhaps 60% or so for every 5% above nominal voltage". So my ET5 is not quite at 5% above nominal so tube life might be reduced a little bit.

Considering those limits, if the relative limits of a 7DJ8 are similar - then it is probably better to use 6922 than 7DJ8 as the 7DJ8 might be under volted and I have since read that under voltage can be very bad for tube life due to potential of cathode poisoning. It can be worse for tube life than over voltage.

The sources for what I have read about how voltage relates to tube life are not authoritative - so they could be wrong. Interesting though.

While I am measuring voltages - I'll add the following which some people might find useful (well I would) and it is not in the ET5 specs:

conrad johnson ET5 power usage measurements:

with mains at 248V 50Hz
about 3 watts idle
power factor while idle 0.49
about 25-30 watts in use
VA 34.6 watts (while power use was about 26)
power factor 0.75
R power 22.8


with mains at 221V 50Hz
2.71 watts idle
power factor while idle 0.49
23 watts in use
VA 30 watts (while power use was about 23)
power factor 0.76
R power 19.4

Anthony

[turntable]

Hi Anthony

Nice measurements and good to know that the voltage does not seen to effect the measures.. I guess it proves that tubes are the problem vs the cj preamp

Cheers

[ronenash]

High heater voltage will shorten tube life considerably. I am not sure why CJ chose this design in the their current line of preamp (ET3, ET5, GAT). The ACT2 AND Premier 14 that I own do not have this problem. If anything I would pull down the heater voltage to 6.0v which is what I chose in my own DIY designs. The tubes last longer and there is no hit in sound quality.
A 7dj8 is definitely a better match for a 6.5v heater voltage IMO.

[plurn]

I sent the measurements to the the conrad johnson service department, and mentioned I had read a lot of reports of tubes going noisy quite quickly in current model cj preamplifiers, and that the previous owner of my ET5 had a tube go noisy within 100 hours. I asked them if my ET5 was ok or if it needed adjustment.

They indicated that all of the measurements are within their design specifications and no adjustments are needed.

They added a note that I may want to experiment with some NOS tubes: Russian, 6n23 and Philips, PCC88

The first one is the robust type that I have seen recommended for preamplifiers that are hard on tubes. PCC88 is equivalent of 7dj8 (7 or 7.3V?).

I received an assortment of tubes from the previous owner of my ET5 so I think I am fine for a while. Will probably give those suggested tubes a go once the goodness has left my existing tubes.

Anthony

[plurn]

I have been using an electro-harmonix gold 6922 (date mark 1212) in my ET5 and have been recording the hours used. By about 345 to 350 hours of use, I have noticed it has started to produce a constant even hiss (not sure if this is what is referred to as tube rush?) which can be heard about 2 feet away from my speakers, even at low volumes on the ET5.

My speakers are quite inefficient at 86dB/2.83v and my power amplifier has 26dB gain. My system is less susceptible to this issue than it might be for others with more efficient speakers. I expect people with more efficient speakers would hear this hiss at the listening position and would consider these tubes failed.

350 hours is really not a lot of time for a tube to last.

I'll keep using this one, for a while anyway, as in my system it still sounds good at the listening position and I want to see how it progresses.

Anthony