6922, a 6DJ8 replacement??

[SY]

If you've got an unstable circuit, what's the issue with putting a couple of 5 cent resistors in? Far cheaper than changing potentiometers and far more effective.

[denny9167]

Originally Posted by SY

If you've got an unstable circuit, what's the issue with putting a couple of 5 cent resistors in? Far cheaper than changing potentiometers and far more effective.

What size would you recommend for the grid stoppers?

[SY]

1k is a safe value. Carbon comp are the traditional choices. The important thing is to have the resistor body as tightly close to the grid pin as possible.

[DF96]

The fact that it oscillates at zero volume confirms that a grid stopper will cure it. At present your volume pot is acting as a stopper, except at zero when it is a short.

The ECC88 family has high gain up to UHF frequencies, so it sees any short piece of wire as a resonator. Combine that with the usual follower instability and you have problems. Add grid and cathode stoppers and all will be well. Personally, I wouldn't worry about carbon comp - you don't need especially low inductance as all you are trying to do is damp an oscillation by adding some resistance.

[mb-de]

In a ECC88/6DJ8/E88CC/6922/6N23P/other "family members"-Cathode follower, a grid stopper is mandatory, and a cathode stopper is highly recommended - 22..47 Ohms will do nicely.

Paranoid people like me add small ferrite beads over any lead to the socket except for the shield connection, or even a small anode stopper (10..47 Ohms were mentioned as effective by Tim de Paravicini in a discussion I had with him a few years ago)...

Parasitic oscillation of cathode followers is very commonplace - sometimes the only noticeable effect is a seemingly microphonic stage, as the cathode follower has effectively become a RF condenser microphone. Sometimes one gets 'buzz', 'whistle' or increased distortion - effects vary...

Regards,

Michael
=->

[SemperFi]

The heater current in EH6922 is 375mA, so they are not true E88CC clones. (Clearly EH wants us to think they are, or they wouldn't call them 6922, but rather 6DJ8 which is probably more likely what they are). I've got 100 of the EH6922s and haven't had one bad yet. I've got a handful of NOS types also, and honestly can't hear much difference. As mentioned, grid stoppers are a must.

[planet10]

Originally Posted by SY

With this tube family, a grid-stopper resistor is almost mandatory and a cathode stopper is often helpful, especially with the 100% feedback of a cathode follower. You also need local bypassing. Intermittent oscillations can manifest as all sorts of noises and odd effects.

Just started this reading this thread. Oscillation was going to be my 1st suggestion. I have a 6922 pre, that was originally for 12AU7. When it was converted no gridstoppers were added. There was a 1.6 MHz oscillation. Grid stoppers cleaned that up (and advanced the performance of the pre).

dave

[Vincent77]

Another difference between ECC88 and 6922 is that the 6922 (and the E88CC) can be microphonic. The 6922 wasn't meant for audio, so it doesn't have any anti-vibration mica springs (which the ECC88 has).

So the 6922/E88CC *may* be prone to shrill or emphasized high frequencies caused by microphony.

The best tube of the family is by far the E188CC, but it is expensive...

[DF96]

I don't think the ECC88 was meant for audio either, but it was meant for small signal work.

[scott17]

Originally Posted by SemperFi

The heater current in EH6922 is 375mA, so they are not true E88CC clones. (Clearly EH wants us to think they are, or they wouldn't call them 6922, but rather 6DJ8 which is probably more likely what they are). I've got 100 of the EH6922s and haven't had one bad yet. I've got a handful of NOS types also, and honestly can't hear much difference. As mentioned, grid stoppers are a must.

Have you actually measured the EH6922 at 375mA? The spec sheet says "not less than 285mA, not more than 335mA". Also, the EH6922 is a 6N23P-EV clone according to the manufacturer.