vintageHIWATTconvention.com

Greetings...new member here!

I recently purchased a Sound City 100 PA Mark 2 amp from a private seller in the UK. I am aware of the Dave Reeves connection with the original SC100 ("Mark 1") amps, as well as his (likely) involvement with the elusive Mark 2 models. The Hylight serial tag on the rear of this PA chassis shows the model number DR116 with a serial number of 318. I've taken many pics of the amp and uploaded them here:

http://s1072.photobucket.com/user/E-Roc ... rial%20318

Transformers are labeled TG5479 and G7650 (output) and TG7084 and G7651 (main). I'm not a tech and have never owned a vintage Hiwatt (I do own a SC MK3). That said, I do believe this may be the only SC Mark 2 PA amp to surface in recent years.

I've reached out to Mark Huss, who confirmed that this amp does appear to have been assembled by Dave Reeves himself in '67 or '68. Does anyone have any further insight into the circuit design or have any pics/schematics of similar early Hylight PA amps?

My intention is to bring this amp back to life and use it for guitar - I'm hoping it sounds similar to an original SC100 ("Mark 1"). The power cord has been cut and so I cannot power it up at this time. The previous owner kept the amp in storage since 1987 and claims it has never been serviced. My local tech is excellent with vintage British amps, and so I plan on having him re-cap it, replace the power cord, and give the amp a thorough checkup ASAP.

Does anyone have any further advice?

Enjoy the pics!

CONGRATS on the amp! i watched that one to the end when it was listed on ebay...

http://www.ebay.com/itm/Sound-City-100- ... true&rt=nc

contacted the forum leader formerly known as Dr. HIWATT (now Dr. HI-TONE ) about this one. def a Reeves wired amp. But you already knew that. fingers crossed the knowledgeable folk around these parts can point you in the right direction and help you get this beast back up and running. you're doing exactly what i had planned for it. repair and restore internally, then play the SHITE out of it.

best of luck mang!!!

-cody

I had one exactly like yours and own a 73 DR112 PA 100.
The Sound City was ice pick bright.The Hiwatt sounds very similar to my old 74 DR103.Both had partridge's and Mullards.
I don't know why they sounded so different.
Heres some pics of my ex DR103 and my DR112.
Dr103


Dr112

Update: my tech is currently in the process of restoring this amp, but he has a question for the experts:

"I need to know the value of the large green voltage dropping resistor (choke resistor, for lack of a better description). It's a 10w resistor, looks to me like it is common to all MK2 SC amps. I think its 750 or 780 ohms. Can you confirm with a SC/HW expert? The other dropping resistors are 6k8 2w & 100R 5w."

So, does anyone happen to know the correct value of the large green "choke resistor" he is referring to? I'm assuming it is the larger green resistor seen in this pic?



Thanks for any help.

it is a 470R

Thanks, Clayton!

My tech just replied with this:

"I figured out the resistor value. Its 750R. First I tried a blacklight, no good, then a green LED and that worked! So, the values are odd. I haven't come across these values anywhere yet. 750R 10w, 6k8 2w, and 100R 5w. The more common values are 470R 10w, 1k 2w, and 100R 5w. This one is definitely 750R. Is the 6k8 part of the same supply? Because if it's 470R it should be 1k. I'm certain of this."

Thoughts?

The newer SC amps used 6k8 (vs. the Hiwatt 1k value), so I would not be surprised if the older one also used the former value.

The 750R is odd, but it's an older amp, so perhaps the 470R value had not yet been settled at that time.

--mark

Thanks, Mark!

My tech and I have discussed changing the screen resistors from the stock 100R 1/2w to 1k 5w to better protect the EL34s…any reason NOT to? The DR504 schematic shows 1k, correct? Any real tone/feel difference?

Anytime you change the screen resistance, it will change the characteristics to some extent, most noticeably when you're overdriving the output stage. I don't know if it would sound better or worse, but it may sound slightly different. If you do opt for the 1k 5w, I would jumper the 470/750 ohm resistor, because having both would be a bit too much IMO.

--mark