Hi all.
I need an equilvalant valve for 6G8. I cannot see a good reason for not using a 6B8
Any thoughts on tbis, I do not have a replacement 6G8.

These are similar and pin interchangeable: But!

Watch the numbers 6G8 suggest metal, 6G8G is liable to be glass & if its GT an internal shield. I think 6B8 is similar?

That would mean that GT & metal have pin 1 grounded the glass "S" type not & they would likely need a shield?

Thanks Marcc

Marc is correct in that the 6B8 is pin for pin for the 6G8 but there is a difference.

The 6B8 is a high gain, sharp cut-off pentode whereas the 6G8 is a remote cut-off ('supercontrol") type intended for smooth AGC operation.

The 6B8 behaviour might be a little "cranky" in your radio if it has AGC around it.

Fortunately most uses of a 6G8G will be used as an audio preamp, and in such cases a 6B8G will be perfectly ok.

There's nothing wrong with giving it a go - if it doesn't work, at least it won't make anything worse.

I assume you've already checked all the components around the existing 6G8G, particularly for open-circuit resistors.

The biggest resistor attrition in that area are the plate resistors of the 6B8's etc. and the grid leaks & Grid stoppers (where used) of the output valves.

The 6G8 had an open circuit filament.

Have you applied heat to the filament pins.
Internal to the pin dry joints, was a common problem with these vintage valves.
And add solder of course.
JJ

The 6B8 is normally used as an audio preamp., the 6G8 as an AGC-controlled IF amp. For audio the 6B8 is a better choice.

I'm still waiting to find out if the 6B8G worked, or even if it was attempted.

Unfortunately we don't know what we have? There are around five different ways to wire the Detector first audio & the choice of tube can relate to it being reflexed or not. Reflexing sees RF and Audio both going trough the same valve.

Even if its AGC attack is a bit different it will at least give an indication as to the sets potential to run.

In reply to Robbert and Marcc.
Yes I needed it for the Little General Rebuild.
Please read my additional post on the Little General. It has been a very long time since I had to get so close and personal with the nitty gritty of valves and have forgotten most of what I new I am rather ashamed to admitt. The set is dead on the front end I now have to retrace what I have done. Not sure if I have wired it up wrong or I have a component problem.

In reply to Johnny.
That was a good suggestion I had not thought of. I have since tried resoldering the pins however it is still oc.

There are swift ways of ,finding where superhets are dead; And, it can be adapted to TRF. Aside from checking voltage, one feeds low IF signal into the pentagrid if that works, you have a dead oscillator, or some other issue up front. I normally use an Oscilloscope as the signal detector, as it can be the signal tracer.

If that alignment method works, make sure that the oscillator tickler coil is not reverse wired?

Hi Marcc.
I have already tried that to no avail.
I need to recheck my circuit.
I have posted more on the Little General post I started previously.