Scott 299b rectifier question

[Jenkster]

I am the proud new owner of a box stock 299b. I am in the process, with some help, of replacing the selenium rectifier. My question is should I use a bridge rectifier will diodes do the trick? I read somewhere that if you use diodes a resistor needs to added? Any help would be greatly appreciated!

Thanks

 

[vendo81]

Yes you can replace your old selenium with diodes or a full wave rectifier that you can get at your local radio shack. Full wave, part # 276-1173 is rated at 4A, 400V and is $2.59 or you can use 1N4007 diodes (1000V rating) if you need more than 400V. You will need to add a 10 watt resistor of the proper value to get the B+ closer to what your 299B needs as the output will be higher than what is coming out of the existing selenium. I usually start at about 100 ohms and measure with the B+ disconnected. A schematic should give the proper voltage needed :yes:

 

[Jenkster]

Thanks vendo81, that gives me the info I need. We are going to replace the filter caps as well. I am going to try and leave it as stock as is possible. For now, since the stock output tubes are pretty weak, I am going with some Sovtec EL84M's that I already have. May go with NOS 7189's eventually. Oh, the Scott labeled 6BL8 tested as new and the rectifier is an RCA labeled Mullard!:thmbsp: The 12AX7A's are strong Tungsols! Can't wait to get it up and running my Wharfedale W70's!

 

[kvflyer]

Thanks vendo81, that gives me the info I need. We are going to replace the filter caps as well. I am going to try and leave it as stock as is possible. For now, since the stock output tubes are pretty weak, I am going with some Sovtec EL84M's that I already have. May go with NOS 7189's eventually. Oh, the Scott labeled 6BL8 tested as new and the rectifier is an RCA labeled Mullard!:thmbsp: The 12AX7A's are strong Tungsols! Can't wait to get it up and running my Wharfedale W70's!

Very good choice of speakers too.

I replace the Siemens selenium bridge rectifier with the 8 Amp, 400 volt bridge from Radio Shack. It has a hole in the center that can mount it. You may have to remove temporarily the the power transformer to put the screw through the hole of the bridge.

I replace the original 1-Watt 10 Ω first resistor (on a 299B) after the bridge with a 22 Ω 5-watt wire wound resistor. I have done many Scott 299 series amplifiers and that usually gets the bias voltage and 12AX7 filament voltages right where they should be. I use a variac and adjust it to 117 VAC before making measurements and compare them to the HH Scott schematic. Some of the other 299 series amplifiers use a 18 Ω resistor after the bridge and I replace that one with a 33Ω resistor however.

That Radio Shack bridge is less than $3 so I keep many on hand.

 

[kvflyer]

BTW, excellent results with the Soviet Military 6pi14pi-ev (6П14П -ЕВ) tubes. Several sellers on that auction site sell them. Often go for about $10 each. However, I do admit to having some NOS GE 7189A tubes :thmbsp:

 

[jandg]

I run the TUFF Ei el-84's in mine. These are great amps without dought. You have a great amp & speaker combo going on, should be nothin but fun for ya. The 299b also has a great to me phono stage as a bonus.
Joe

 

[diamondsouled]

Howdy Jenster,

You might be better going with the Russian 6pi14pi-ev (6П14П -ЕВ) tubes that KV mentioned rather than the Sovtek EL84M's; they are a sturdier tube and more like a 7189 than the regular Sovteks.

Lar

 

[Jenkster]

Thanks for all the info. guys, man I love this site! My friend, who is working on the amp, is a bit of a novice when it comes to home stuff. He has fixed many a guitar and keyboard tube amp though. He did get his old Sherwood receiver up and running like new. What a mass of wires, caps, resistors etc. in that thing!

I found a real good deal on a pair of Klipsch Forte' II's that are very temping. I would still keep the Wharfedales but I Like the idea of horns with tubes.:scratch2: