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HH Scott 299c

hogwylde09

hogwylde09

Vintage Tube Hi-Fi Rules
Subscriber
I’ve established a baseline of operation. It’s no virgin either, with some sections in power supply & bias caps being bypassed. Also a 100 ohm dropper been added in place of a chalk. In looking at Hamseed’s site nothing will be available until 2022. I’m wondering wth they can find (LK72) kit, 33uf/550v caps to stuff their cans. I’m seeing stocks are running low for even 33/500 Mouser & Digi-Key ( Nichicon).
I looked yesterday, they may be gone today.
Have lots of pencil type, but top out at 350/450 volts. Those won’t suffice in this Scott.
I run my Fisher 400 on a line bucker I built. Really helps keep those 7868’s run cooler.
With the higher voltages’ on the Scott, what about a couple of CL-90 in series? Maybe would not have to build another bucker.
 

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Correct me if I'm wrong but those Scotts (and my LK48) all use 450 volt capacitors. Of course higher voltage rating is fine but I think your 450 will work if you cannot find anything else.
 
The 299C/D used 500 WVDC electrolytic capacitors after the GZ34 in many applications. I do se some versions of the 299C using 475 WVDC filters.
 
Some versions use 30 µFD X 2 for the first filter. JJ makes a 32 µFD capacitor which is rated 500 WVDC. They do not state the temperature on them though. I have used them in many amplifiers, LK-48, LK-72, 299C/D etc. with absolutely no problems. They do require a clamp which does not look original. But Japanese equipment used clamp-mount capacitors so that is not too uncommon.
 
hogwylde09 said:
I’ve established a baseline of operation. It’s no virgin either, with some sections in power supply & bias caps being bypassed. Also a 100 ohm dropper been added in place of a chalk. In looking at Hamseed’s site nothing will be available until 2022. I’m wondering wth they can find (LK72) kit, 33uf/550v caps to stuff their cans. I’m seeing stocks are running low for even 33/500 Mouser & Digi-Key ( Nichicon).
I looked yesterday, they may be gone today.
Have lots of pencil type, but top out at 350/450 volts. Those won’t suffice in this Scott.
I run my Fisher 400 on a line bucker I built. Really helps keep those 7868’s run cooler.
With the higher voltages’ on the Scott, what about a couple of CL-90 in series? Maybe would not have to build another bucker.
Click to expand...

The exposed high voltage lead on top of the square wire wound resistor in your bottom left picture is a fatality waiting to happen.
You need to get some heat resistant insulation on it, or build a protective cage around it.
 
Most of the CE Distribution can caps are rated to 525vdc. It is only the very first section of the Power supply that sees anything close to 450+ . And the GZ34 will controlled the Voltage ramp up. I used all CE can caps to restore a 233 which was really closer to the 299d as per the schematic. There was no problem. The reversed polarity Bias can is another issue. I did build a Bucking transformer and used it for awhile, but found it was really unnecessary. I have also tried the CL90 in several amplifiers and for some odd reason did not like the sound afterwards. Although I do have one installed in my CJ Premier 11a and really cannot tell a difference in sound.
 
Pablodeux said:
The exposed high voltage lead on top of the square wire wound resistor in your bottom left picture is a fatality waiting to happen.
You need to get some heat resistant insulation on it, or build a protective cage around it.
Click to expand...
Sure right about that too. I have looked at a few schematic, seems like the first dropping resistor should be around a 20 ohm 10 watt. I don’t have a clue as to why this was put in. My first impression was maybe the original snapped off. Who knows.
I remember digging around in a parts house and buying a couple upright chassis mount round style.
I know this 120 ohm most likely drops too much. Hopefully I will be able to find a 30-40 ohm. After the cans are stuffed, I can play with voltages.
 

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You might try that 120 Ω resistor because with today's higher line voltages, it might just work out. They do make some square ceramic resistors with the leads coming out of the end. I have seen some guys clamp them in place similarly to the Standee resistors.
 
kvflyer said:
You might try that 120 Ω resistor because with today's higher line voltages, it might just work out. They do make some square ceramic resistors with the leads coming out of the end. I have seen some guys clamp them in place similarly to the Standee resistors.
Click to expand...
I've called where I picked up that 120 ohm. There's a 20 & 31ohm 30 watt available. Their vintage used is bargain bin priced, maybe a buck or two each. Gonna dig through the old short shaft slotted Claristat pots. They would be excellent candidates for the balance & bias I intend to replace.

Just a kid in a candy store
 
This is OT for the this model, but significant, nonetheless. I have had two LK-48 amplifiers that had the bias pot messed with. In one, someone had put a two-gang pot in place and crisscrossed connections for whatever reason. I had a spare used 1-meg pot and thankfully, the parts/wires had not been shortened, so it went back together as it should. Another one had the pot completely missing and the wires tacked together. Since I did not talk to whomever did that to either, who knows why? Maybe the pot was frozen and they didn't attempt to get it going.

I have carefully used heat and eventually, that old grease lets go and the pot works. But it took several attempts and patience.
 
kvflyer said:
This is OT for the this model, but significant, nonetheless. I have had two LK-48 amplifiers that had the bias pot messed with. In one, someone had put a two-gang pot in place and crisscrossed connections for whatever reason. I had a spare used 1-meg pot and thankfully, the parts/wires had not been shortened, so it went back together as it should. Another one had the pot completely missing and the wires tacked together. Since I did not talk to whomever did that to either, who knows why? Maybe the pot was frozen and they didn't attempt to get it going.

I have carefully used heat and eventually, that old grease lets go and the pot works. But it took several attempts and patience.
Click to expand...
While establishing a baseline of operation, I changed the old selenium and those two 4uf/250 caps. I was still trying to chase down awful hum. I carefully bypassed the rest of the PS sections via a 10uf/500 with jumper wire and a test lead probe. No dice.
I marked the balance and bias pots and did see the -voltage change a small amount. However these pots seem awful flimsy built in construction. I do want some better. So naturally my thoughts jumped to those old AB or Clarostat heavy duty ones. I do intend to add 10 ohm bias sense resistors and test point jacks.
Now back to the hum. In reading a post Scott 222c
March 10 2010, the Standee resistor is discussed.
Just maybe the “dangerous” sand dropper’s composition is not up to the job of canceling out the high pulse it’s (from the ideas from @Mike Stehr). Page 12 or 13.
Again today while sorting through the vintage used at my parts house, I will most likely buy up all the inventory of this Standee or equivalent chalk style.
Maybe whoever had this unit in the past just simply gave up from inability to cure this hum, which sounds to me like 60hz. Could be wrong though.
 
Trying to find some sort of schematic for this 299c, or whatever it is. Is there a database here on AK?
Not a 33 ohm resistor to be found anywhere. 3.3 ohm at the output transformers.
It's has the TR13-2-1 138217E PT. At 117vac I have 500volts on the plates, 475 grids, and -21 bias after stuffing the cans.
What have I gotten myself into this time...
 
Interesting to note that the 299C came in no less than 7 various configurations. Some look very much like the 233 and the later models would be very similar to the LK-72-B or 299D. Not all schematics are out there. You might have to look at a couple and use the closest one or even multiple schematics.

I have an LK-72-B on the bench right now.
 
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