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Bullseye
| | Posted on Saturday, August 02, 2003 - 1:32 pm: | 
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Well I need 1 tube actually. I have an old Black Cat modulator that my Dad gave me but the tube went bad in it. What I need is an 8417 vaccum tube. If any of you guys have or know where I can get them please let me know or Email me at cws1325@att.net. I know this is'nt the email address in my profile but I changed ISP's and forgot to update my profile before I cancelled my other service.
Forum Master Note : I have changed your email address on your profile to the one listed above.
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Skilletlicker
| | Posted on Saturday, August 02, 2003 - 3:32 pm: |
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www.tubesandmore.com has the 8417 tube listed on page 14 of their catalog
thanks skilletlicker |
Bullseye
| | Posted on Saturday, August 02, 2003 - 7:33 pm: |
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Thanks Skilletlicker for the info. and Thank to you Forum Master for fixing my profile. I'll do my best not to let it happen again! |
2600
| | Posted on Sunday, August 03, 2003 - 2:53 am: |
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Be sure to check the zener diode in the corner near where the power cord enters the rear panel. It might have two 1-Watt zeners in series, or just a single one. If the old tube shorted inside when it failed, they might have been clobbererd. If this happens, the tube will either overheat and "cherry", glowing visibly red on the OUTSIDE metal parts in the tube (there SHOULD be a gentle orange glow fromt the very center ONLY). It will do this either:
1: Immediately as the tube warms up, overheating on standby even before you key it, or:
2: Just as soon as you key it, even with the carrier turned WAY down.
When a 8417 tube fails inside a Black Cat amplifier, short-circuit current may flow to ground THROUGH those little zeners, and they become a permanent dead short when they fail. This removes the (approx) 35 Volts of NEGATIVE-polarity control voltage from pin #5 of the tube socket. This voltage holds the tube's current down to a safe level. If the zener(s) are shorted, that control voltage goes away, and your (expensive) new tube will commit suicide before the second or third time you key it. Not fun. Not cheap, either.
If you have a voltmeter, clip the negative end to the metal bat-handle of a front-panel switch. Remove ALL the tubes, and turn on the power. Set the meter to DC Volts, and touch the other probe to pin 5 on the underside of the large tube socket. You should read at least 30 Volts, and usually less than 40 Volts. If you are using a digital meter, it should show a minus sign, showing that this is a negative-polarity voltage you are hooked to. If you have an older, analog (needle) Volt meter, the positive lead gets clipped to ground, and the negative lead goes to pin 5. Otherwise the needle will pin to the left. If the reading is under 30 Volts, you are skating on thin ice if you install the tube and try to use the thing.
The pin numbers are (faintly) molded into the plastic socket body. If they are too faint, the rule is easy to remember. Find the polarizing (key) notch in the socket at the rim of the center hole. The pin to the right of the notch is pin #1. Count clockwise from there to pin 5.
The quality of 8417 tubes that you can buy now, 15 years after they were discontinued isn't as high as it was when the amplifier was made. I typically suggest buying two, to improve your odds of getting one good tube. Black Cat squeezed every last Watt out of that tube that they could. The stress this creates will clobber a tube that isn't nearly perfect. A tube that is perfectly okay in a guitar amplifier running at 400 Volts may break down in a linear running the tube at 800 Volts, like the Black Cat stuff does. It may not look like it, but it's a genuine radio "hot-rod" of a box. Just a small hot rod, that's all.
73 |
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