Hi - I just fitted some new valves to my Audio Innovations 500 amp, Sovtek
5881s, and they work very well, nice 'punchy' sound compared to the EL34s
they replaced. It's an 'autobiasing' amp btw so apparently the swap is OK.

However, they do smell a bit! it's a sort of burning plastic thing, and 2 of
the valves have a yellow residue appear between the valve base and the
glass. The amp has been on for about 20 hours, 5 lots of 4 hours, and the
smell is still there although no more 'seepage' that I've noticed.

Any ideas?!

TIA

Rob

I've noticed this with new tubes too, particularly Chinese 6550's, and 807's.
Turn off the lights, and make sure the plates are not glowing a dull red. If
they're black, and all you can see is the filaments and maybe a little bit of
blue glow, all is well, and the smell will go away with time.

RJH wrote:

Hi - I just fitted some new valves to my Audio Innovations 500 amp, Sovtek
5881s, and they work very well, nice 'punchy' sound compared to the EL34s
they replaced. It's an 'autobiasing' amp btw so apparently the swap is OK.

However, they do smell a bit! it's a sort of burning plastic thing, and 2 of
the valves have a yellow residue appear between the valve base and the
glass. The amp has been on for about 20 hours, 5 lots of 4 hours, and the
smell is still there although no more 'seepage' that I've noticed.

Any ideas?!

TIA

Rob

P.S. Welcome to the wonderful world of the 6L6 family of tubes. They're my
personal favourite tube.... RCA got it right way back in 1936, and if I could
choose only one type of power output tube to live with for the rest of my life, it
would be a 6L6.

Max Holubitsky wrote:

I've noticed this with new tubes too, particularly Chinese 6550's, and 807's.
Turn off the lights, and make sure the plates are not glowing a dull red. If
they're black, and all you can see is the filaments and maybe a little bit of
blue glow, all is well, and the smell will go away with time.

RJH wrote:

Hi - I just fitted some new valves to my Audio Innovations 500 amp, Sovtek
5881s, and they work very well, nice 'punchy' sound compared to the EL34s
they replaced. It's an 'autobiasing' amp btw so apparently the swap is OK.

However, they do smell a bit! it's a sort of burning plastic thing, and 2 of
the valves have a yellow residue appear between the valve base and the
glass. The amp has been on for about 20 hours, 5 lots of 4 hours, and the
smell is still there although no more 'seepage' that I've noticed.

Any ideas?!

TIA

Rob

Max Holubitsky wrote in :

I've noticed this with new tubes too, particularly Chinese 6550's, and
807's. Turn off the lights, and make sure the plates are not glowing a
dull red. If they're black, and all you can see is the filaments and
maybe a little bit of blue glow, all is well, and the smell will go
away with time.

RJH wrote:

Hi - I just fitted some new valves to my Audio Innovations 500 amp,
Sovtek 5881s, and they work very well, nice 'punchy' sound compared
to the EL34s they replaced. It's an 'autobiasing' amp btw so
apparently the swap is OK.

However, they do smell a bit! it's a sort of burning plastic thing,
and 2 of the valves have a yellow residue appear between the valve
base and the glass. The amp has been on for about 20 hours, 5 lots of
4 hours, and the smell is still there although no more 'seepage' that
I've noticed.

Any ideas?!


It may well be the plastic in the bases 'curing'. I have Svetlana's with
bases slowly changing colour with use. Maybe something new manufacturers
can learn from the old NOS designs, is the use of better materials for the
bases? :-)

" wrote:

Max Holubitsky wrote in :

I've noticed this with new tubes too, particularly Chinese 6550's, and
807's. Turn off the lights, and make sure the plates are not glowing a
dull red. If they're black, and all you can see is the filaments and
maybe a little bit of blue glow, all is well, and the smell will go
away with time.

RJH wrote:

Hi - I just fitted some new valves to my Audio Innovations 500 amp,
Sovtek 5881s, and they work very well, nice 'punchy' sound compared
to the EL34s they replaced. It's an 'autobiasing' amp btw so
apparently the swap is OK.

However, they do smell a bit! it's a sort of burning plastic thing,
and 2 of the valves have a yellow residue appear between the valve
base and the glass. The amp has been on for about 20 hours, 5 lots of
4 hours, and the smell is still there although no more 'seepage' that
I've noticed.

Any ideas?!


It may well be the plastic in the bases 'curing'. I have Svetlana's with
bases slowly changing colour with use. Maybe something new manufacturers
can learn from the old NOS designs, is the use of better materials for the
bases? :-)

Ever try a hot biased set of metal 6L6's? I've never smelled anything new that
outgassed that much.

Max Holubitsky wrote:

" wrote:



Max Holubitsky wrote in :



I've noticed this with new tubes too, particularly Chinese 6550's, and
807's. Turn off the lights, and make sure the plates are not glowing a
dull red. If they're black, and all you can see is the filaments and
maybe a little bit of blue glow, all is well, and the smell will go
away with time.

RJH wrote:



Hi - I just fitted some new valves to my Audio Innovations 500 amp,
Sovtek 5881s, and they work very well, nice 'punchy' sound compared
to the EL34s they replaced. It's an 'autobiasing' amp btw so
apparently the swap is OK.

However, they do smell a bit! it's a sort of burning plastic thing,
and 2 of the valves have a yellow residue appear between the valve
base and the glass. The amp has been on for about 20 hours, 5 lots of
4 hours, and the smell is still there although no more 'seepage' that
I've noticed.

Any ideas?!



It may well be the plastic in the bases 'curing'. I have Svetlana's with
bases slowly changing colour with use. Maybe something new manufacturers
can learn from the old NOS designs, is the use of better materials for the
bases? :-)



Ever try a hot biased set of metal 6L6's? I've never smelled anything new that
outgassed that much.



I use those in my MC30s. I had a bias failure and somebody (not me, I
swear!!) put a 15A fuse in the holder. The smell alerted me to the
problem. Fixed the bias problem and the tubes work fine.

Raymond