My "Ugly Betty" Basic M1 Restoration

jheu02

AK Subscriber
Subscriber
This is a continuation (sort of) of a thread I started in Solid State around 2 years ago. I'm beginning to get to the point of really starting work on it, though I want to finish up a SA-8500II I'm working on. That's now delayed due to needing insulator material for a "batwing" output transistor that I found with paper as a substitute.

I wanted a mini project to do, so I made a modded relay as developed in this thread by Leesonic. I was going to test the amp with the new relay, but when I opened it up, I discovered that I had previously desoldered all the outputs and drivers for testing (I'd forgotten I had done that). I don't really want to solder them all back in just to have to desolder and redo the heatsink grease, so further testing will be put on hold til I get this thing cleaned. I'm thinking that the Deep Clean Your Amp sticky might come in handy for this one. Other than possibly removing the transformer, should I also label and remove the Sankens and drivers? Any other hints/tips/cleaners to avoid?

So, here's some photos of my Ugly Betty M1 and the new relay.

15144882110_6a0a08cba5_o.jpg


15331600715_3c7ceedaa2_o.jpg


15308559156_3f39178023_o.jpg


15331597985_4d640f7ff0_o.jpg


15308559326_3d8ce0b689_o.jpg


15331288192_d45bc6c8aa_o.jpg


15331290572_d239098179_o.jpg


New relay
15328436021_888b14487b_o.jpg


15144836829_b9c81a4d9b_o.jpg
 
Ohhh my goodness, what happened to that poor ole amp, looks like it was drug behind someones car!!

Owning a minty one of those amps, its good to see it getting some much needed and deserved love, kenwood m series amps are nice units.
 
Ugly Betty's Makeover Begins

I finally got around to finishing my SA-8500II (except for a plastic switch cover for the Tone Defeat switch if anyone has a parts unit from 1978-1982 era, hint, hint). So, tonight I pulled Betty out, opened her up, and decided to try out the new relay. This meant I had to solder all the outputs back onto the board, but I felt that was the best course of action to see if she'd even come out of protection. Long story short, after all the soldering was done, I first started with a 72W bulb on the DBT. Bright, dim...steady dim. OK, looks good and then went to a 150W. This time it went fully dim since the bulb was "sized" properly. While on this bulb I dialed the bias down to around 2mV each side, powered down, and then got ready for line power. On line power I brought the bias up to 13mV each side. SM gives a fairly broad range of 8-20mV.

1. Any who've restored these...what do you set or does it matter as long as it's in this range?

I then decided to check DC Offset at the speaker terminals. negative 50-60mV was the reading with the positive probe to the positive terminal, neg to neg. reversing the probes gave me positive readings. :scratch2:

2. Why? And more importantly, where should I be looking first to get a more normalized reading there? I wanted to check sound quality, but not with quite that high a reading.

I want to be a little more methodical with this restoration, as in the past I've just started recapping, etc. So, before I even clean the insides I want to get some decent readings as a base line.

I imagine I'll need to start with some voltage readings at various places, but it was late enough I didn't want to really start that tonight. Best plan of action???
 
Betty Sings Purdy

I took a bunch or voltage measurements tonight. All were within 10% of the schematic value. The furthest off were the high voltage rails. Where +/- 68V were supposed to be, I was reading +/- 64.4V. So, I stopped taking measurements and decided to see if I had sound. I used the Pre-Outs from my SA-8500II to feed the inputs of Betty. Source was a familiar CD "Isotopes" by Rusty Squeezebox (pick it up if you can find it). At first I thought I had a bad R channel as there was no sound on that side. Rechecked all connections, still nothing, but I decided to fiddle with the input RCAs while music was playing and got sound. Bad patch cord. Good reminder to check the simple things first before assuming the worst.

So, Betty's makeover just got that much easier. Since she's so dirty inside, I am going to remove the transformer, relay, and maybe the VRs and do a bit of a deep clean per the tutorial before replacing the caps and regreasing the outputs and drivers. Any thoughts on the low voltage?

Also, the schematic values that were supposed to read 0V all measured between -64mV to -72mV. So maybe that has something to do with the negative DC Offset readings.
 
Betty Goes to the Spa (Bath and Sauna Treatment)

Did you get that thing from the bottom of a creek.

No, a Good Will clearance store. Sold as non-working, which turned out to be the relay.

I snipped the transformer leads to remove it, desoldered the VRs (even though I have new multiturns) and relay, and unscrewed some CBs so I could give Betty a good cleaning. She's currently in the sauna (oven) finishing the drying out process.

16301291638_c4e12535eb_b.jpg


16489008895_b5e1f943f3_b.jpg
 
Last edited:
Doh!!!

I got a bunch of work done today. Started first with the power supply caps and getting the transformer hooked back up. Main filter caps are Panasonic TS-HA, and what I put in are 6800uF/50V and 10,000uF/50V. And that's where the Doh comes in. I had been watching leestereo's M1 restoration and he'd increased capacitance of both the low and high voltage caps. Well, I decided just to increase the high voltage rail filters and was just thinking of the cap diameter. Well, height matters too! The caps I put in are just too high...i.e. they'll slightly bend the top of the case if I leave them in.:tears:

All's not lost. I need to place a mouser order for my Sherwood S3000 anyway, and I forgot to order a bipolar and UKL cap for this. So, it won't get finished as soon as I thought.

Other work done was the recap of the main board, removing and cleaning the heat sink and all the OPTs, removing and reinstalling the drivers, changing R1,2 from carbon film to 1/2W metal film, and making some new R61-64 R/C filters for the drivers. They were originally 1/4W 330ohm/100pF. I replaced them with my Dale RN60Cs and new 100pF ceramic caps. These also originally had 1uF/50V 'lytics strapped across each pair which I replaced with 1uF/63V kemet film caps.
 
Betty After Her Spa Day

Most things are now reinstalled. A little extra cleaning of speaker binding posts, chassis where the heat sink was, headphones and speaker select boards, faceplate and cover (though I'll probably strip it to bare metal and repaint it), etc. I'm also planning to run a twisted pair from the inputs to the main board vs. the straight wire that's stock. Mouser order is placed to get shorter caps. Here's how she looks currently.

16507150515_1693b88004_b.jpg
 
That cleaning process you did was really interesting. Seems Ugly Betty has been to a health spa :D

Looks very nice!
 
Betty's All Clean

She just needs some new clothes (i.e. her cover stripped, primed, and repainted). My shorter filter caps arrived during my last trip (TS-HA 8200uF/80V) as well as the Nichicon ES bipolar and KL that I didn't have in the correct value. So, those all got installed, the main circuit board reflowed and cleaned, and the rewiring of the input jacks with twisted leads to the board as well as upgrading the 1/4W carbon film resistors to 1/2W Dale RN60C metal films. Bias is now once again set to 14mV across the resistors and I'm listening to some test disscs using my SA-8500II as the preamp. She'll never be a beauty queen (unless I come across a mint faceplate), but beauty is really on the inside, and with music, how it sounds. And in this regard, I never would have expected this sound from the way she looked when I got her. I now know why folks rave about the basic series.

Pics to follow when I edit them. Full flickr set here

Overhead
16392942108_b1fe7a29d4_b.jpg


Power Supply with right-sized Caps
16393992558_d21f45d707_b.jpg


Re-wired Input Jacks w/ Dale RN60Cs
15959073924_4fa4dc0b46_b.jpg


Right Side Detailed
16395360419_e770348914_b.jpg


More Right Side Detail
15961447413_45489a6abf_b.jpg


Board Detail
16395359749_4880e0c5ab_b.jpg


Listening Test
15959072714_b0f64a0d5b_b.jpg


Anybody got a nice faceplate from a parts unit???
 
Last edited:
No faceplate from a parts unit but I used a black felt tip marker to take out the scratched areas in mine. You could get away with that until you find one especially if its going to be in a dimly lit room.
 
Betty's New Dress

Thanks Lee. I finally got around to doing the current source mod as I'd forgotten to order the LM334Zs originally. I also got the cover stripped, primed, and the initial paint coats (though I'll want to do one more when it's warmer). Currently listening to Acoustic Alchemy's Back on the Case. Very nice detail. Pioneer SA-8500II as the Preamp, a Sony CDP, and some EPI 100s I restored. The inverted domes are singing sweetly!

16523120367_ca068ced7b_b.jpg


It still would be nice to have a more pristine faceplate. So, if anyone comes across a parts unit that's got one in good shape, let me know. The black marker isn't cutting it. I may end up masking-off the face and spraying the edges. Thoughts?
 
Back
Top Bottom