175 DLH

[analogman]

I have had a run of bad luck with a particular tube amp BLOWING tubes (shorts) (KT88s). Now, I think I am hearing a problem with one of my 175 DLHs. It seems to be there on certain frequencies, and at higher volume (forte dynamics). Is there a specific test tone frequency or source material such as "pink noise" that I can use to determine with some degree of certainty if there is in fact a problem? I am not an equiped E.T., but I do have a number of test and technical recordings. I would also like to avoid opening them up for inspection, unless a repair is indicated as they are untouched originals.
What I think I'm hearing is an excessive harshness, not quite a buzz, but sort of a high frequency roughness that wasn't there before. May just be that I'm hypersensitive to it now after the tube failures. Can a powerful shot of impulse noise like that from a shorted tube blowing a fuse split or crack a diaphragm, or just smoke the coil?
Thank you for your consideration,
Analogman

[Earl K]

- Sorry to say , but when amplifiers go "BANG" in the night, the following pic shows the usual result to the diaphragm ( these things are fragile ) .

- Forget using Pink Noise .

- One wants to listen to a pure "Sine Wave" at upwards of 1 volt ,( measured by a DVM/DMM at the drivers terminals ) with tones swept from @ 650 hz up to 3 or 4 Khz . Actually a tenth of this voltage is more than loud enough for my ears and will usually reveal most problems .

- With this sine-wave tone sweep , distortion and/or a cracked & broken surround will manifest themselves in any manner of unpleasant sounds .

- If you need new diaphragms or have any doubts about checking yours / I'd suggest taking them to a qualified professional . If you personally install new diaphragms , any implied JBL warranty is null & void .

[analogman]

- Sorry to say , but when amplifiers go "BANG" in the night, the following pic shows the usual result to the diaphragm ( these things are fragile ) .

- Forget using Pink Noise .

- One wants to listen to a pure "Sine Wave" at upwards of 1 volt ,( measured by a DVM/DMM at the drivers terminals ) with tones swept from @ 650 hz up to 3 or 4 Khz . Actually a tenth of this voltage is more than loud enough for my ears and will usually reveal most problems .

- With this sine-wave tone sweep , distortion and/or a cracked & broken surround will manifest themselves in any manner of unpleasant sounds .

- If you need new diaphragms or have any doubts about checking yours / I'd suggest taking them to a qualified professional . If you personally install new diaphragms , any implied JBL warranty is null & void .


I don't have a pure "Sine Wave" recording but I do have some warble tones, bass, treble and high frequency decades etc. (like Stereophools Test CD #2). Seems to do OK. I'm just hearing some harshness, added "grit" or haze that wasn't there before
Could the diaphragm in the picture you provided even be capable of producing anything, other than possibly noise?
Thank you for taking the time to respond to my question.
Regards,
Analogman