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HH Scott 222c Power Tubes Issue....

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So I played the amp for 6 hours straight today. Checked the bias a couple times and it was good. Checked the amp periodically by hand to make sure it wasn't getting too hot and it was normal every time.

After a few hours I took the 7189 Preferred Tubes out and rolled in a brand new quad of EL84M's I got from Tube Depot quite a few years ago. Set the bias after about 20-30 minutes and it set fine/normal. Nothing erratic.....checked the bias a couple hours later and it was real close. These tubes sound great.....which reminded me of why about 8 years ago I bought a couple of extra quads because I really liked them in this amp.

At this point everything seems totally normal since now running the amp a total of 18 hours since the tube redplated. I won't take it for granted though.....I still plan on having it checked out and won't leave it unattended while it's on

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Oh, and I've cleaned the tube pins and sockets a couple of times with Deoxit since the redplate.

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 Last night put in a RCA rectifier tube in this 222C just to hear if there might be any audio improvement and the RCA flashed a blue and white color internally, and the amp died.  Slow-blow fuse is intact.  Now it won't even power up 😥Guess it's time for a full service job on this.  Why in the world would a blown tube take out the whole amplifier?

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 Do the tube heaters still light up? If so you probably blew the very first cement wire wound resistor in the B+ directly connected to the 5AR4 rectifier output.  If the heaters don't light up the amp is not getting power for some reason. Check that fuse for continuity with a meter. Those old original slo blo fuses can blow but not show obvious visual signs of it. 

 

 If the amp is still original it's long past the time it should have been restored so yes I'd suggest getting it properly rebuilt. 

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On ‎11‎/‎5‎/‎2018 at 1:00 PM, NOSValves said:

Those old original slo blo fuses can blow but not show obvious visual signs of it. 

Exactly the situation.  It appears fine and exhibits no continuity.  Thanks for the remedy!  Back to life again.

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Exactly the situation.  It appears fine and exhibits no continuity.  Thanks for the remedy!  Back to life again.
That's good news.....glad to hear you're up and running.

My 222c has been acting totally normal and sounds great since the redplate. I've been rolling tubes like it's a sport. Every time I've changed power tubes that's basically the only time I check/adjust the bias and it exhibits normal behavior like before.

I also got back into the habit of cleaning the tube pins and sockets. I clean the tube pins with deoxit and a brass bristled brush every time I make a change. The sockets get deoxit much less often.

At the time that the EL84 redplated, I had just gotten back into listening to this amp after quite a while of diving in deep with my ss gear. I misplaced my brass bristled brush and I might not have even given anything a shot of Deoxit. So, like some had said....maybe it was a dirty pin/socket thing and that's what caused the redplating. I don't know but since then everything has been totally cool as far as the bias and how good the amp performs.

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Yup probably oxidized sockets and tube pins! 
Craig....PM sent.

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While we're on the subject of 222's and tubes, OP, what tubes have you been rolling in and what do you think?

 

I had three good Telefunken tubes, and a few RCA 7189s laying around, both sounded nice. Teles we're nearly magic. But, I'm not made of money, so I changed the screen grids feeder resistor to somewhere around 3K and dropped the voltage there to about 320. JJ EL84 sound quite lovely with that change. The first quad went 14 months as my main stereo/theater amplifier until the rectifier blew. (New rectifier and a fuse got it back running, but I didn't want the renter's grubby hands on it.)

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10 minutes ago, DirtyErnie said:

While we're on the subject of 222's and tubes, OP, what tubes have you been rolling in and what do you think?

 

I had three good Telefunken tubes, and a few RCA 7189s laying around, both sounded nice. Teles we're nearly magic. But, I'm not made of money, so I changed the screen grids feeder resistor to somewhere around 3K and dropped the voltage there to about 320. JJ EL84 sound quite lovely with that change. The first quad went 14 months as my main stereo/theater amplifier until the rectifier blew. (New rectifier and a fuse got it back running, but I didn't want the renter's grubby hands on it.)

Renter?

Nice landlord to provide vintage stereo equipment!

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4 hours ago, muel said:

Renter?

Nice landlord to provide vintage stereo equipment!

Yeah, one of those "I'm a single guy with a house and some dude from my church needs a place to live for a while" things.

 

I learned so much about Nibiru and chemtrails while he was here...

 

😑

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Just wanted to follow up to say that I finally had my tech check out the amp and everything under the hood is fine.

I feel like a fool because I was not biasing properly. Also, I was not balancing the channels. He set me straight and it is simple. The amp sounds great and the bias is stable.

I played the amp today for about 12 hours straight and my concern that it might be running too hot was put to an end. He said the power supply should run about 150 degrees Fahrenheit. Checking it throughout the day it was a consistent 140 degrees and the OT's about 10 degrees cooler.

What a relief.

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So now some  time has passed after rolling a variety of tube brands through your 222c...any updates?  What pre/power combination do you prefer?  How many brands are in use  now?  Which aren't so good? 

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So now some  time has passed after rolling a variety of tube brands through your 222c...any updates?  What pre/power combination do you prefer?  How many brands are in use  now?  Which aren't so good? 
Well, pretty much all the new production tubes I've tried just didn't cut it compared to my NOS tubes. I tried Mullard, Genelex, Sovtek and Psvane (Treasure series) 12AX7's and only the Psvane's give the NOS a run for their money.

I tried The Tube Store 5AR4 Preferred Series 5AR4 and it was promising at first but my NOS Amperex GZ34's just sound so much better in my amp.

I'll keep the Psvane's as back-ups but the NOS tubes have proven themselves over and over in my 222c.

At this point I've settled on:

NOS Mullard 12AX7 long plates (preamp)
NOS GE 6U8's (phase inverter)
NOS RCA 7189's (power)
NOS Amperex Bugle Boy GZ34 (rectifier)

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Siemens E80CF sound really good as subs for the 6U8's. I used them for a few years. I could go either way. I still want to try other types of 6U8 tubes.

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I did like the EL84M power tubes. Now that I've spent quite a bit of time with the NOS RCA 7189's in the amp I'll go back to the EL84M's to evaluate.

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On 12/16/2018 at 7:00 PM, SWL said:

I feel like a fool because I was not biasing properly. Also, I was not balancing the channels. He set me straight and it is simple.

 

Curious about this.  Was it process oriented?  Have a 222C also with the test points and adjustment screws above the chassis that Craig put in. (bias balance and bias voltage)  I go by his process instructions cheat sheet.  

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