Crack 5998 low volume

[m17xr2b]

Hi everybody. I have an issue with my crack. For the past few months I have using it with 6080 and 5814 tubes. In that time I have installed speedball and update the output capacitors and installed a bypass on the last cap in the power supply. I used Mundorf Mkp 100uf 250V for the output caps and 2.2uf 250v for the bypass. Today I just got a NOS Chatham 5998. When I played some music I noticed that the volume was very very very low. I have to crank the crack to max just and I'm just able to hear sound. Could this be because of the output caps and the bypass. The rest of my tubes 6080's work as they should and I know the 5998 has different specification. So it is the tube or the crack?

[adamct]

That's odd. I've done the same thing you have (replaced output caps and bypassed last cap on the power supply), and I'm also running a 5998. No problems at all. With 7 o'clock as my zero position, I usually listen around 9 or 10 o'clock. It sounds like your tube must somehow be bad, although I've never heard of the situation you're describing before. Try cleaning the pins on your 5998, and recheck your RCA connections.

Best regards,
Adam

[m17xr2b]

I have already cleaned the pins and I don't think that the rca connections are bad because with all my other tubes the amp works as it should, no issues at all. Also the tube lights up so no issues there.

[Paul Birkeland]

The rest of my tubes 6080's work as they should and I know the 5998 has different specification. So it is the tube or the crack?

If every tube works except one, then the amplifier is working properly but the tube is not.

[m17xr2b]

I forgot to say that it worked for the first ten minutes. In that time I felt that my tube search had come to an end. After that the left channel died and after and then the sound faded. I have to place the volume knob at half to just about hear some sound. I do hear both channel.

[Doc B.]

If the other tubes work, it is a bad 5998.

[Paul Joppa]

If you want you can check the 5998 pin voltages - I expect pins 3 and 8 will be incorrect (too low) indicating  an exhausted cathode.

[BNAL]

Have you tried putting the 6080 back in to see if that is working?

[m17xr2b]

Yes they all work. I guess I will have to send it back for a replacement and it's a long way from Romania to the US.

[adamct]

Where did you buy your 5998 from? Oddly enough, I recently (last week) bought a quad of 5998s, and last night I realized I had the same issue with one of them. I bought my tubes from vacuumtubes.net.

[m17xr2b]

hmmm.... me also

[adamct]

They probably won't make you send it back, but it is obviously annoying to have to wait for the replacement. And I don't get how they send out bad tubes...

[m17xr2b]

They told me to send the tube back in order to get a replacement.

[m17xr2b]

Just got my replacement tube from tubemaze. While I did that I ordered another 5998 as a spare. Tested the tubes. I just have to mention that I did not receive 5998 but chatham 2399. So one tube has sound in only one channel. The other tube works good but my god it's microphonic. If i tap the table where the crack is very lite I can clearly hear it in the headphones. Also the microphonics do not start right away as I power on the crack but after about half an hour. The other tube that I use is a CBS 5814WA that I used for a while and I know it's not the culprit. I also noticed that the microphonic effect is intermittent. Is this a known issue with 2399 tubes?

[adamct]

I have not experienced that with any of my 2399s (or 5998s, which are identical).

I have run into a problem of my own. I was using a Bendix 6080WB and a Tungsram E80CC. E sound was perfect. Today, I received two G.E.C. 6AS7Gs I had been waiting for. The seller tested them at 102% and 104%, respectively. I pulled the 6080WB and inserted one of the G.E.C.s. The sound was very, very low and static-y.  I let the tube warm up, but there was no improvement. So I pulled that tube and inserted the other G.E.C.  Same problem. I figured I got a pair of bad tubes, so I decided to insert a 7236 I had and knew was good. To my surprise, I had the same problem: low, faint, scratchy sound. I pulled the 7236 and inserted a 2nd 7236. Same problem. Ten I swapped in the 6080WB I had been listening to. Still no improvement. I figured, "O.K., must be that the E80CC went bad." To I pulled it and inserted a spare E80CC. STILL NO IMPROVEMENT. WTF?!?!?

Anybody have any ideas what the problem could be? FWIW, the tubes are all glowing. I also hear sound in both channels, but both are low and scratchy. And last night everything sounded perfectly fine. What is going on?