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Q & A / Re: Did I Blow My 200s?
« Last post by Isaac on Today at 08:03:43 am »
Good luck.
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Q & A / Re: Did I Blow My 200s?
« Last post by Smoothwound on Yesterday at 06:28:53 pm »
Thank you Isaac. I have the original Mulard KT-88's I can try.

I'll let you know what happened. If not, I'll take it to Hal at Guitronics in SF.

best,
Dave
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Q & A / Re: Did I Blow My 200s?
« Last post by Isaac on Yesterday at 08:47:50 am »
Here's how I'd start off. First, disconnect the monitor and hook up the amp per normal and try it. I assume you've already done this, and that's when you got the horrible cranking noise. Next, I'd measure the resistance of the speaker, just to make sure it's all right (no strong reason to think otherwise at this point, but it's an easy check). Try a known good amp on the speaker. If it works, then you've proven the speaker and the cord. Try the 200S on a known good speaker (if the 200S cabinet tested good, then you're already there, as you tested it above). If you've reached this point, then you've proved that the problem is in the 200S head.

The head powers on, so you know it's not the fuse. loudthud mentioned flashes of light in the big tubes. Take that a step further: do they look normal? I had one go bad a few months ago. It had white ash inside. The other didn't. The two power tubes didn't look the same. I don't think one bad tube is your problem, though. Both, maybe.

Do you have spare tubes? If so, replace the tubes. If the amp works, then replace the original tubes one at a time. That is, turn the amp off, let the tubes cool, take one out and put the original back in. Turn the amp on, then test it. Tedious and time consuming, but effective. When the amp stops working, then the last tube you put in is bad. Replace it.

Everything I've described so far, anyone can do. If replacing the tubes doesn't solve the problem, then it's deeper, and more specialized knowledge is required, specifically an amp tech. I assume that you are not an amp tech, so, at this point, I'd suggest you take the amp to someone who is.
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Q & A / Re: Did I Blow My 200s?
« Last post by Smoothwound on Yesterday at 07:22:54 am »
The speaker I normally use was always plugged in. It is the original cab with JBL's. It worked before I plugged in the wedge, then no sound after.
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Classified / Look for Beta head box
« Last post by keuf on Yesterday at 04:27:14 am »
Looking for an empty case for Beta head (see pict). I'm in France!
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Q & A / Re: Did I Blow My 200s?
« Last post by loudthud on July 17, 2018, 07:58:03 pm »
Try the amp with the speaker you normally use. Same noise? Do you see any flashes of light in the big tubes?
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Q & A / Did I Blow My 200s?
« Last post by Smoothwound on July 17, 2018, 05:44:54 pm »
Hello everyone, its been awhile since I've been here as I have been playing my 200s with love for years since I first acquired it. Now I may have gone and done a stupid thing. We acquired a floor monitor for free, which I think (and I know I should have taken a pic of this before i posted) said 100 watts 8 ohm. It looked passive. So I plugged it into the external speaker to see if I could get my speaker and it working together. Next thing I know the 200s is dead. If I turned it all the way up to 7 it made this horrible cranking noise. Did I mess it up for good? Please tell me its just a fuse or tube or something.

thanks for any and all help on this one.

Dave
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Q & A / Re: 6AN8A Substitute/Replacement
« Last post by Soundmasterg on July 17, 2018, 01:07:29 pm »
The 7199 is similar enough that with some socket rewiring it would work in the circuit without major changes. However they are very expensive these days and the new manufacture ones aren't very good.

Any change to a twin triode like a 12AX7 would change the gain structure of the amp considerably, especially if you stayed with the gain stage + cathodyne inverter setup like the Sunn has. If you went with a long tail pair arrangement or a floating paraphase inverter arrangement then some of the gain could be brought back but I still think there would be a net loss as the pentode in the 6AN8 supplies a lot of gain. That would also be a major change to the amp and would require some troubleshooting and voicing time to dial it in sufficiently.

There are probably some other triode pentodes that could be used, but I don't know of any offhand. The 6AN8 supply is still good for NOS stuff and will likely be for quite awhile. I wouldn't worry about it that much myself. Its not a tube that is used in a ton of stuff so the supply won't dry up super fast.

Greg
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Q & A / Re: 6AN8A Substitute/Replacement
« Last post by GrannyGremlin on July 17, 2018, 11:22:19 am »
It can be done, but personally I love 6AN8s.  It is half pentode half triode vs dual triode like a 12A_7 so it would be a significant mod.

There are no drop-in substitutes, but there are workalikes: 7258 (same pinout but diff heater current 13.5V vs 6.3 so nonstarter I'd think) and the 6AV8 (diff pinout - not a hard change).

I coulda swore the 6JW8/ECF802 was a drop in compatible but looks like it isn't.  The pinout is very different at least.

Anyway, as the OP said, they are not too expensive and there is still supply.  Not hugely in demand.  I just buy them up whenever I come across them (have a few things besides my Sunn amps that use them) - last year I came across a NOS Rogers 5 pack (rebranded RCAs) in a local radio repair shop and snapped it up.
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Q & A / Re: 6AN8A Substitute/Replacement
« Last post by Isaac on July 17, 2018, 08:25:44 am »
The original Model T uses a 12AX7 as a phase inverter. I have toyed with the idea of converting one of my older amps to that configuration, but I haven't done it.
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