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Old 14th January 2016, 12:53 AM   #1
BobSchott is offline BobSchott
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Default Bille 300b upgrade has high B+

HI all

I own an original set of 300b Billies. Finally did the mu, gridchoke, and ultrapath upgrades. (I know, I know, I'm going way back in time but the upgrade package sat for years with moving, kids growing up, college, etc, etc).

I've completed the upgrades and in checking voltages I noticed that the voltages in the amp are high. Main AC in is 124VAC here in NYC, B+ in both amps is 483/484, B++ to 6sn7 is 377/382 and 300b plate is 475/477. VAC off the pwr trany at the recitifier is 800VAC or 400 per side which is def high.

The only PSU mods were the addition of the big 10uf cap right after the 82R that follows the rectifier tube. Also moved the choke to right after that 10uf cap and 82R rather than where it originally was - between the pairs of smoothing caps.

I'm assuming that part of this is the high mains VAC here in NY. I think these voltages are a bit high for rolling my NOS tubes. Right now I'm running the amps with the VA tubes that it came with originally.

Thoughts on how to bring those voltages down so that my tubes will last longer?

btw, before I modded the second amp I checked voltages on the original amp before mods and they were the same as the modded version - give or take a couple of volts.

Thanks you all

Bob
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Old 16th January 2016, 02:17 AM   #2
BobSchott is offline BobSchott
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As a follow up, I've been doing some research on adding another choke. Seems that will bring down B+ and some say it's a better solution than resistance. Anyone care to add to this idea. I need to come down about 35 volts.
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Old 5th February 2016, 07:53 PM   #3
Bdubois61 is offline Bdubois61
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Sorry you're not getting any other responses. I bought my billies back in 2001/2002 and had the same voltage issues. Here in NC a/c was about the same as yours. I bolted a wirewound to the chassis and soldered it in to the input line pre-transformer. Not optimal but it worked. I did the mu mod but haven't done the grid choke or ultrapath yet. Have those mods been worth it to you?
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Old 8th February 2016, 09:13 PM   #4
BobSchott is offline BobSchott
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Quote:
Originally Posted by Bdubois61 View Post
Sorry you're not getting any other responses. I bought my billies back in 2001/2002 and had the same voltage issues. Here in NC a/c was about the same as yours. I bolted a wirewound to the chassis and soldered it in to the input line pre-transformer. Not optimal but it worked. I did the mu mod but haven't done the grid choke or ultrapath yet. Have those mods been worth it to you?

I added a 10 ohm 12 watt wirewound to the mains in - from the ac receptacle to the switch. Lowered AC into the power tranny from 123 to 116 and brought B+ down to around 450 and B++ to 463. That's a cheap fix for now. Gonna build a little power distribution box with an 8.5 V 4A bucking transformer in series with the load that'll bring mains down to 117. I think I'll even front panel switch those mains so that I don't have to reach around the back of the amps to turn off using the tiny power switch. Probably have the 123V mains also unswitched for the other rack componenets.
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Old 22nd February 2016, 05:45 PM   #5
BobSchott is offline BobSchott
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Join Date: Nov 2015
Quote:
Originally Posted by Bdubois61 View Post
Sorry you're not getting any other responses. I bought my billies back in 2001/2002 and had the same voltage issues. Here in NC a/c was about the same as yours. I bolted a wirewound to the chassis and soldered it in to the input line pre-transformer. Not optimal but it worked. I did the mu mod but haven't done the grid choke or ultrapath yet. Have those mods been worth it to you?
I think the choke and ultrapath are good mods but I did not do critical comparison so I can't say to what degree they helped or the sound changed. After all the mods I can say that I'm very pleased with the sound of the amps. fwiw, the choke and mu are not that expensive. If you stick with the Obligato caps. The ultrapath can get expensive if you go with boutique caps. btw, my ultrapth setup is 47uf for the 300b cathode cap and 12uf for the ultrapath cap to B+. What I gathered from all the mod comments is that you want about a 4or 5:1 ratio between those caps.

Best

Bob
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