Playing with my Scott

[DirtyErnie]

Got some holiday-season Funemployment time on my hands, so it's time to get the lab sorted out and working better. 

First order of business: music.

 Had the 222c running as the main amp upstairs for a while, then marriage and kids decided on simpler things that don't burn small hands. Also, it popped a JJ rectifier and always buzzed after, kinda helps the decision.

 

I'll add a pic and more after I get on the computer, cell phone pix are too big to attach...

 

More:

Looks like it's time to replace the screen bypass caps on the 6GH8's, one finally went way off spec.  Pretty sure I've heard these are prone to failure.

There's one more failed cap in the phono stage, but since it's under everything AND I don't use the phono stage, it gets to just hang out and be failed.

 

Previous repairs & mods:  Replaced the two positive-voltage cap cans with JJ equivalents.  Although the main HV cap is a 40-20-20-20.  Currently, there's a small 10uf-500v as the first cap after the rectifier, then an 80-ohm resistor, then 60uf of that cap feeding the output transformer center taps.  Not sure what difference that made, but things seem to be OK.  10UF should be easy on a GZ34.

 

I added a tag board (barely visible, upper left) with some trimpots to get independent bias voltage adjustments on each channel.  

 

Screen Grid voltage was about 390 at first, way too high.  Swapped out the 1.2K series resistor for a 3K, working with the stock 8K shunt resistor as a voltage divider for the screens.  Added another 10uf - 500v cap to bypass the 8K to ground and add a little filtering at that node.  With the original Telefunkens in one channel (I have all four, but the screen pin busted off one of them.  Yes, I could cry...) it sounded amazing stock, but with what tubes are available at my budget point (JJ), there was a harshness.  With screen voltage closer to 300v, the JJ's sound very nice.  I'm a firm believer that load impedance and screen voltages should match for best sound, and 390v had the JJ's WAY off their map.

 

Then there's the standard 'replace the selenium rectifier with a silicon bridge and adjust the series resistor after it' for the pre-amp tubes heater supply and output bias voltage.

 

Also swapped out the original driver-to-output caps with russian Paper-in-oil types, but made sure to wrap them in heat-shrink to keep their steel bodies from shorting out the insides of my amp.

 

Planned: I'm intending to add a little outboard input & volume box to direct feed the power amps through a pair of RCA jacks I'll install somewhere on it, I think I found a place right behind the volume knob that should work.

 

Maybe I'll build a cabinet for it some day.  That's another thing my 20-year-old self did that I don't want to talk about 22 years later...

 

 

[OO1]

4 minutes ago, DirtyErnie said:

Got some holiday-season Funemployment time on my hands, so it's time to get the lab sorted out and working better. 

First order of business: music.

 Had the 222c running as the main amp upstairs for a while, then marriage and kids decided on simpler things that don't burn small hands. Also, it popped a JJ rectifier and always buzzed after, kinda helps the decision.

 

I'll add a pic and more after I get on the computer, cell phone pix are too big to attach...

 

For  a Scott 222C   , you must do a total recap , the older wiring  is prone to failure  , I would recommend you to replace it completely if you wish to avoid problems in the future -

 

  and given the more modern parts available today , the result would be even better than expected , this particular amplifier model can yield a crystal clear sound   , be very careful with the Faceplate and knobs of these units ---  good luck with your project -if you have any questions --feel free to reach out

[DirtyErnie]

17 minutes ago, RandyH000 said:

For  a Scott 222C   , you must do a total recap , the older wiring  is prone to failure  , I would recommend you to replace it completely if you wish to avoid problems in the future -

 

  and given the more modern parts available today , the result would be even better than expected , this particular amplifier model can yield a crystal clear sound   , be very careful with the Faceplate and knobs of these units ---  good luck with your project -if you have any questions --feel free to reach out

 

After the first round of mods, I was hearing things I'd never heard before in movies I was quite familiar with, and 60's vintage music was amazing.  Probably something about being recorded with tube consoles, and being played on a tube amp.  Axis: Bold as Love was nearly a perfect experience.

This was on a pair of upgraded KG 2.5's and a JBL 12" active sub box coming out the 'center' channel.