I have a pretty extensive collection of tube data manuals that I kept in the event that I could not locate something online and I still use them from time to time.
I could not locate any information in any of my tube manuals or online.
Are you sure you've got the right part number?
Base? (B9 - 9 pin miniature, octal, loktal, noval, etc.)
Can you provide the manufacturer and post some pictures?
My initial thought was that the 5BL8 might be a 5V filament voltage version of the 6BL8 which is a common triode/pentode used in audio and RF applications like VHF TV tuners and FM front ends... But you state it is a rectifier...
I have seen 5BL8 triode/pentodes in the past, but have no data on them.
I could not locate any information in any of my tube manuals or online.
Are you sure you've got the right part number?
Base? (B9 - 9 pin miniature, octal, loktal, noval, etc.)
Can you provide the manufacturer and post some pictures?
My initial thought was that the 5BL8 might be a 5V filament voltage version of the 6BL8 which is a common triode/pentode used in audio and RF applications like VHF TV tuners and FM front ends... But you state it is a rectifier...
I have seen 5BL8 triode/pentodes in the past, but have no data on them.
My apologies. It is a 6BL8. My tube tester setup chart goes from 6BL7 to 6BM5. These are located near the 7189 (EL84) section of a H.H. Scott model 299-B power Amp. It is currently blowing the 3 Amp fuses. I have tested all the other tubes and the results are favorable. The 6BL8s (two of them) are the only remaining tubes to test. Any ideas? Thank you for looking into those tubes for me!
Frank’s suggestion is good. If you can test as 6U8 you will be close enough to rule that out as a problem. 6U8, 6GH8 and 6BL8 are close, but not the same. They are used in the amplifier section as voltage amp and phase splitter, so I suspect there is a problem somewhere else. Have you checked the bias at around -15V?
Good luck.
Good luck.
Capacitors, the actual rectifier and bias supply are all suspects. Power transformers in these models do occasionally short - usually one of the HV taps.
Does the fuse still blow when you remove the 5AR4 rectifier tube? If it does not your power transformer is probably OK. I would use a "dim bulb tester" to limit the current to the amplifier to a safe value to prevent further damage while diagnosing/repairing. (100W lamp in series with load)
Note the bias filter cap on these models has a positive case ground, and there are no modern equivalents, but you can restuff the can with small radial capacitors. The other caps can be replaced with modern equivalents or close equivalents from antique electronic supply and elsewhere.
Many of these amps used ceramic coupling capacitors, but if not the originals will probably be leaky at this point.
Does the fuse still blow when you remove the 5AR4 rectifier tube? If it does not your power transformer is probably OK. I would use a "dim bulb tester" to limit the current to the amplifier to a safe value to prevent further damage while diagnosing/repairing. (100W lamp in series with load)
Note the bias filter cap on these models has a positive case ground, and there are no modern equivalents, but you can restuff the can with small radial capacitors. The other caps can be replaced with modern equivalents or close equivalents from antique electronic supply and elsewhere.
Many of these amps used ceramic coupling capacitors, but if not the originals will probably be leaky at this point.
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