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SIEGMUND BIG BOY 300

#8
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So I made a few changes from the stock unit.

Added a Jensen Di
Upgraded to 400 watts. Using 6 KT 150's
Went with a darker walnut and a vented top
Black and white control plate with led back light

Pics so far.
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#16
BassmanPaul said:
Sorry Duke but I didn’t like the distortion showing up in the videos. Might well be in the recording chain though. I sincerely hope you get yeoman service out of your new amplifier.
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Sounds like preamp drive to me.

To my understanding, ultra-linear is not ideal for output drive, rather more designed to produce max clean power. As a result, I am surprised 6 KT120 gives 300 watts and 6 KT150 gives 400 watts. This is plenty of power, but I believe Trace V6 and Reeves 400 get >400 watts from 6 KT88s. 6 KT120 or 6 KT150 should be able to produce significantly more power in an optimized ultra-linear circuit.

The construction looks nice and I would enjoy auditioning the amp. I look forward to the review.
 
#17
Wasnex said:
Sounds like preamp drive to me.

To my understanding, ultra-linear is not ideal for output drive, rather more designed to produce max clean power. As a result, I am surprised 6 KT120 gives 300 watts and 6 KT150 gives 400 watts. This is plenty of power, but I believe Trace V6 and Reeves 400 get >400 watts from 6 KT88s. 6 KT120 or 6 KT150 should be able to produce significantly more power in an optimized ultra-linear circuit.

The construction looks nice and I would enjoy auditioning the amp. I look forward to the review.
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Yeah, the plan was to get a 'clean' 400 watts, we think it could get and the transformers can handle significantly more, somewhere near 540. But the plan was clean power...I've said 400 just to be safe...my mesa strategy is 435 with 8 kt88's ,

Also, I've heard other clips of the overdrive that are very very good. The ef86, has a lot to do with the od. I have several nos ef806s that I'm sure will be super sweet. I also prefer to get my od from my pedals, just my personal taste....

Agreed about the vent, but this may never leave my studio, so I was ok with the vent, it was actually my idea...

The builder, Chris has been exceptional to work with and I'm very, very happy with the build and his expertise
 
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#18
DirtyDuke said:
Yeah, the plan was to get a 'clean' 400 watts, we think it could get and the transformers can handle significantly more, somewhere near 540. But the plan was clean power...I've said 400 just to be safe...my mesa strategy is 435 with 8 kt88's ,

Also, I've heard other clips of the overdrive that are very very good. The ef86, has a lot to do with the od. I have several nos ef806s that I'm sure will be super sweet. I also prefer to get my od from my pedals, just my personal taste....

Agreed about the vent, but this may never leave my studio, so I was ok with the vent, it was actually my idea...

The builder, Chris has been exceptional to work with and I'm very, very happy with the build and his expertise
Click to expand...

I wouldn't be surprised to see significantly more than 400 watts, but it really depends on how the circuit is setup rather than just the tubes. Regardless that's a lot of power, especially for basement jamming. I am sure the amp will be awesome!

The components are packed pretty tight on the chassis, so good ventilation is going to be critical. I had to install a small case fan on one of my amps to keep the output tubes from running away.

The amp is touted as class A but I believe it is probably AB1. The original designer liked to bias his creations at 117%. The amp came to me biased at the factory spec and the tubes burned out fairly quickly. Factory Spec is -52V bias....with no mention of current. I am currently running the amp at 90% dissipation with about -60V bias, so you know it was running hot at -52V.

After the original tubes went out, I bought a bias meter and installed some new tubes. After about an hour of operation, I noticed the amp would start to loose bias and current would start picking up even when the amp was biased around 60%. Thermal runaway occurs when the control grid gets so hot that it starts emitting electrons and acting like a second cathode. Basically the current flow between grid and plates pulls the bias down so the tube red plates.

The problem is partly low air circulation as the case is pretty tight. I think the company quit making the amp because it was super hard on tubes and they are purest who don't believe in fans. The tubes were getting so hot that the tolex on the rear panel was starting to melt. I installed a small case fan blowing on the tubes and the amp sounds great and holds 90% bias as long I care to play.

Hopefully you won't need to worry about heat with the large vent on your amp. If you do, check out the Cooler Guys. I used this kit and it is very quiet: Coolerguys Dual 80mm Fan Cooling Kit | Coolerguys
 
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#19
Yes. We have discussed a fan and the air movement. From our conversations he sets everything up to run very conservatively and cool.

I request the venting and the fan. But since the front and back are grill cloth and the back is open, with the fan I believe we are very very safe

Sorry to hear about your issues.
 
#20
DirtyDuke said:
Yes. We have discussed a fan and the air movement. From our conversations he sets everything up to run very conservatively and cool.

I request the venting and the fan. But since the front and back are grill cloth and the back is open, with the fan I believe we are very very safe

Sorry to hear about your issues.
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No worries, in my experience tube amps sometimes need to be "sorted" a bit.

When do you expect to get your finished Big Boy? I look forward to your review and it will be interesting to hear how it compares to your Strategy.
 
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