Author Topic: 1970's Sound City 200 Plus (Read 9193 times)

plexi50 · « **on:** December 30, 2014, 03:46:34 pm »

I have a 70's Sound City 200 plus. (4) KT88 power tubes. I dont see the power tube plate voltage on the schematic i have found.
I am reading 660VDC on my fluke DVM. Scarry! I am also using an oven mitten while probing the voltages.
Does anyone have readable voltage specs or a schematic with more detail?

HotBluePlates · « **Reply #1 on:** December 30, 2014, 03:51:09 pm »

The schematic in the Hoffman Library shows 620v for the power supply node connected to the OT center-tap, so 660vdc sounds right.

The screen voltage should be half, given the stacked power supply.

plexi50 · « **Reply #2 on:** December 30, 2014, 03:54:03 pm »

Thanks HBP. Let me go look at that schematic again/

eleventeen · « **Reply #3 on:** December 30, 2014, 06:17:10 pm »

That's funny. I usually play with an oven mitt on my left hand. It really makes barre chords sound nice and warm.

plexi50 · « **Reply #4 on:** December 31, 2014, 08:07:50 pm »

The amp sounds loud and proud after a biasing of the KT88 power tubes. I have a very nasty pop when i use the sensitivity switch. Cathode/
The gain really drops quite a bit using it.

Ritchie200 · « **Reply #5 on:** January 02, 2015, 10:48:50 am »

WOW! From the small shot of the faceplate, it looks REALLY clean! Do you have the head cabinet too? Is this one yours or are you working on it for someone? Please post some more pics!

On a side note, take a close look at the bottoms of all your supply caps to make sure they are not ready to take a dump - its about time... What KT88's are you running in it?

Jim

Ritchie200 · « **Reply #6 on:** January 02, 2015, 11:58:09 am »

Ok, your going to have to help me and my old eyes out... I can not find a sensitivity switch on the schemo (is it marked Jojokeo?

Sorry...). Also, what is with all the preset pots in the tone stack? I don't think I've ever seen this before?

Jim

plexi50 · « **Reply #7 on:** January 02, 2015, 01:19:34 pm »

Ritchie200 It is a SC Plus Mark 4 model and a little different than the early model. The odd part for me on this amp is the way the speaker output jacks work. And the inputs with attenuation and the Slave jacks. Sort of confusing when looking at the input and speaker out jacks. It is an amp i worked on for someone. The customer supplied EH KT88 tubes. Very clean amp over all. Heres some more pic's.

Looking through my folders i forgot to take complete pic's of the cab and amp in it's case.
Ive been procrastinating lately taking complete pic's of the amps i have worked on this past year. I got to get back in gear

plexi50 · « **Reply #8 on:** January 03, 2015, 03:16:38 pm »

I got the amp back to do a full power supply re-cap. Any recommendations on the filter cap cans i can use? These are (2) lead caps. One positive and one negative. I will be sure to take many more pic's this time/

Also have to make all four speaker outputs rewired in parallel to one another.

plexi50 · « **Reply #9 on:** January 04, 2015, 09:20:54 am »

I found single radial cans. ARS. http://www.arselectronics.com/ARSWEB/CapPage2.html#radial

Ritchie200 · « **Reply #10 on:** January 04, 2015, 09:18:54 pm »

What is the voltage rating on the originals?

Jim

TubeGeek · « **Reply #11 on:** January 05, 2015, 12:53:19 am »

Nice amp. Someday I hope to see one of these on my bench!

plexi50 · « **Reply #12 on:** January 05, 2015, 07:52:28 am »

Quote from: Ritchie200 on January 04, 2015, 09:18:54 pm

What is the voltage rating on the originals?

Jim

The original caps are (1) X2 16uf 450VDC / (3) 200uf 350VDC & (3) 200UF 450VDC.
The amp is pretty heavy Tube Geek so put on a back brace if you see one.
Man i wish they built everything like they used to. It's a nice piece of work for sure.

Ritchie200 · « **Reply #13 on:** January 05, 2015, 09:56:33 am »

Haha! I just noticed the 200 watt headphone jack!

Caps look like a good swap. Check diameter to see if you need different clamps.

Jim

ps You do realize with a cap job your SOP testing should include 5 minutes of volume on 10 Pete Townsend windmill chords. Please record and post.

TubeGeek · « **Reply #14 on:** January 05, 2015, 05:06:54 pm »

Jeez I love the guts of these and Hiwatt's.

I just replaced 6 of those Erie cap cans inside a Marshall Master PA. I don't know much about them but they seem to be good quality caps.

~~Are 200uF cap cans still manufactured?~~ I see your link already posted.

Looks like a fun job to me!

Thanks for sharing pics! More the better in my opinion

plexi50 · « **Reply #15 on:** January 07, 2015, 02:34:41 pm »

I received the ARS capacitors today and am very pleased with there size being closer to the originals that i thought they might be.
A sigh of relief. Putting them in later today/

TubeGeek · « **Reply #16 on:** January 07, 2015, 02:58:18 pm »

It's always nice when that happens!

plexi50 · « **Reply #17 on:** January 07, 2015, 03:18:30 pm »

It's always nice when this happens!

Ritchie200 · « **Reply #18 on:** January 07, 2015, 04:15:18 pm »

Wooohooo! Lookin' good!

Jim

Ritchie200 · « **Reply #19 on:** January 07, 2015, 04:18:04 pm »

Sorry, tell your client that after an EXHAUSTIVE search and after pulling in a few favors, you were able to find these EXTREMELY rare replacements that fit perfectly.

Jim

plexi50 · « **Reply #20 on:** January 07, 2015, 05:00:30 pm »

Oh yeah!!!! Im so happy with ARS. Finished with installing the PS caps. Have to wait on the bias caps that will be here tomorrow. I forgot to order them when i ordered the PS caps. Dah/

smackoj · « **Reply #21 on:** January 07, 2015, 08:50:40 pm »

I'll bet the lights go dim when the guitar player hits "standby" on that hunchback hee man! I'd like to take that to the rest home with me the next time we do the Polka and Bingo Mixer.

plexi50 · « **Reply #22 on:** January 08, 2015, 02:24:08 pm »

Got the bias caps in and done. This thing is a dam fire breathing dragon.
The best way to describe the amp is to call an Ampeg V4 /SVT a loud and deep roar.
The Sound City 200 Plus is a THUNDEROUS EARTH MOVER. Honestly i couldn't use it period except for Air Raid announcement's

It's a real living monster. The chassis gets so hot after 30 minutes that you can not touch it without getting badly burned.
Im not going to try it. I could make a video of it cooking a small piece of bacon though. Im serious!

TubeGeek · « **Reply #23 on:** January 08, 2015, 02:29:52 pm »

Someone is trying to talk me into building a 200W or 400W version for his bass rig.

I have been mulling it over and then I saw this post and became more intrigued.

I fell in love with hiwatt's ever since I built my own DR504 a few years back.

plexi50 · « **Reply #24 on:** January 08, 2015, 02:43:31 pm »

Do you think the customer would mind if i made BLT on his chassis?

TubeGeek · « **Reply #25 on:** January 08, 2015, 02:46:38 pm »

Quote from: plexi50 on January 08, 2015, 02:43:31 pm

Do you think the customer would mind if i made BLT on his chassis?

Maybe I'll charge extra for the convenience of cooking bacon on the side.

plexi50 · « **Reply #26 on:** January 08, 2015, 03:15:09 pm »

I really would make a video of it cooking bacon but then my customer might get the urge eat every time he plugged in his amp.

plexi50 · « **Reply #27 on:** January 08, 2015, 09:41:29 pm »

OK all BLT to the side. The sensitivity switch has a very nasty pop when used. Personally if it were mine i would get rid of this cathode switch. But for owners sake what can i do to make this switch more user friendly?

navdave · « **Reply #28 on:** January 09, 2015, 01:27:10 am »

Did you recently buy this on ebay? Seen one just like it with no tubes in it was gonna get it for $1500 but I backed out. CLEAN......!

plexi50 · « **Reply #29 on:** January 09, 2015, 08:47:26 am »

Quote from: navdave on January 09, 2015, 01:27:10 am

Did you recently buy this on ebay? Seen one just like it with no tubes in it was gonna get it for $1500 but I backed out. CLEAN......!

No i didn't.

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Author Topic: 1970's Sound City 200 Plus (Read 9193 times)