Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Feb Sun 26, 2017 8:03 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 55 posts ]  Go to page 1, 2, 3  Next
Author Message
 Post subject: HH Scott LK-60 Calibration and Restore [56k Warning!]
PostPosted: Mar Sun 10, 2013 7:06 pm 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
Hey guys,

I recently got an HH Scott LK-60 amp and after much cleaning and re-seating the transistors,etc. it finally works great. However, there are two adjustment pots for each channel and according to the schematic sticker on the chassis one is for adjusting Bias and the other for Balance.

I do not own the service manual, so I have no idea how to fine tune these. The amp sounds fine and there are no issues, but I would like to properly readjust everything.

If anyone has a scan of the calibration routine, please let me know. A full scan of the entire manual would be better, but I have not found anything on the internet except people selling scans for $30(!)

Thanks in advance!


Last edited by Maraakate on Jun Sat 22, 2013 5:27 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 5:56 am 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
bumping this, hoping someone can help out!


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 6:51 am 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
http://www.alohaserve.net/tubestuff/1fo ... artial.pdf

Partial manual shows the balance & bias adjustment.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 6:06 pm 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
Thanks. It took me a while to find it (not an ace at reading these schematics yet) but the resistors are the ceramic block style (I know I'm using incorrect terms) under the unit. There's 4 of them and they read TRU-OHM .82. Just put the leads to them and adjust accordingly for 0.17mv +/-4.

The only thing I'm caught on now is adjusting the Balance. The manual states:

"With no signal input and 8 ohm loads connected
across the speaker outputs, measure voltage on case
of output transistor Q10-Q110 (68-72 volts). Set volt-
age at collector of lower output transistors Q11 Left
Channel, and Q111 Right Channel, for one-half sup-
ply voltage, approximately 35 volts, using Balance
Adjust R6 (A3 Left Channel Driver PC Board) and
R6 (A103 Right Channel Driver PC Board). Variations
of +/- 1/2 volt due to line voltage fluctuations are normal."

The transistors themselves are the ones that are attached to the large heatsinks and I know where the R6 adjusters are but I have no idea how to measure these? Besides setting my DVM to Volts, removing inputs, and add 8 ohm load (aka just setting up a pair of 8 ohm speakers) but where do I attach the probes?

Thanks for your help so far.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 6:54 pm 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
Maraakate wrote:
measure voltage on case of output transistor Q10-Q110 (68-72 volts).

but where do I attach the probes?

- lead to ground
+ lead to the metal case of a output transistor

be careful not to short any output transistor to ground


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 7:26 pm 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
Got it all dialed in. Thanks for your help!

The only remaining issue is the right channel on the Phono is quiet (it's not dead, but the volume must be loud to really hear it). I tried swapping the only socketed transistor on those two boards and still had the issue. I don't see any obvious leakage from the capacitors, but I am assuming that side must be rebuilt? I'm unsure of what I should check on it besides that. There's no obvious short wires, etc. that I see.

Extra and Tuner work perfectly running from my computer. I tested running my turntable into a an external preamp and attached it to the Extra input and it worked fine too so I can rule out the turntable and RCA cables.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 8:18 pm 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
Compare the voltages from the working channel to the non-working channel.

And yes, I recommend you re-cap all the boards with audio-quality caps.
Attachment:
lk60-volt-ck-1.jpg
lk60-volt-ck-1.jpg [ 102.77 KiB | Viewed 2957 times ]


Last edited by hawaii.ken on Jul Fri 12, 2013 8:15 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 8:29 pm 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
I will give it a test later tonight when I get home from work. Same deal as before, negative to ground/metal chassis and positive to one of these points on the schematic?

A recap is planned at some point, though I should do it sooner than later because they are indeed from 1965 so they're reliability at this point is very questionable, :P.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Thu 25, 2013 8:49 pm 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
Maraakate wrote:
Same deal as before, negative to ground/metal chassis and positive to one of these points on the schematic?
Yes


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 4:06 am 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
I did test all of them and they were in spec except 25V read about 22~23V on both sides.

[i]However[i/], I started probing from both sides of each cap and found that the 2MFD 25V Cap (C1) was reading a different value for the voltage on the negative side. I replaced it with a 1uF 50V, and then 2.2uF 25V to test and the volume did get louder but it still wasn't where it needed to be. I know it's not the right thing, but I put a 10uF 50V in there and it didn't get any louder, the volume stayed consistent with each cap.

I guess the rest of the caps on that board need replacing too? They all read about the same +/- sides compared to the others except for C1. I didn't test the 2 paper caps though nor the values of the resistors as I would have to desolder a leg from each one to test.

Not sure what the next step is here?

EDIT: I also forgot to add the the bass is almost non-existant on the channel. Turning the bass all the way up does bring it in a bit but it's nowhere near the same level as the other channel. Again, all these problems are gone via Tuner/Extra so it's something with the preamp board or something running it to it and I have been sure to clean all the switches, pots, etc more than once they are all good to go.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 5:12 am 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
Check that the knob on the balance control is properly installed (balance control rotates equally in both directions).

Do the voltage readings on the tone control board, comparing the good channel with the not-good channel.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 5:25 am 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
Balance is proper, I will have ot check the Tone tomorrow but I think it is okay because treble and bass work properly on the Tuner/Extra inputs.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 6:11 am 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
Did a check anyways... plot thickens because on the tone control board the two 25MFD 25Volts on the channel that has issues have been replaced with different brand capacitors that aren't consistent with the rest of the design. On their negative sides they read extremely low millivolt values, just like the issue on the preamp board that had the faulty capacitor.

Went ahead and checked the Drive output boards as well and everything there is entirely within spec for both sides.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 6:40 am 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
I recommend that you re-cap with Audio Grade Electrolytic Capacitors such as these:
http://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/_/N-75hqt?P=1yztuat

Replace film caps with polystyrene or polypropylene.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 7:21 am 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
I found a thread over at AudioKarma where a fellow listed Mouser parts list to replace the Electrolytics with TVA Atoms. I will just use those as the price seems okay and they are specifically meant for radio, tv, and audio equipment.

For the film caps, I have no idea of the values on them or how they are read. Could you tell me the ones that would need replaced on the Preamp and Tone boards and how to read them properly for future reference?

Thanks for all your help and quick responses so far!


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 7:41 am 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
When you said Film I thought you were talking about the Ceramic flat disc ones. These are the ones I want to know how to read. Apparently, these very rarely fail.

Which ones are the film caps? I was planning to replace all the axial lead paper and electrolytics minus the 3 huge socketed ones as nothing was leaking from those and power output is fine.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 7:51 am 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
TVA Atoms are great for power supply applications (to replace axial lead paper caps) but not so great in the audio signal path.

Ceramic flat disc caps usually don't need changing.

Can you post some pictures of the amp & boards?


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 7:57 am 
Member
User avatar

Joined: Mar Sun 10, 2013 7:03 pm
Posts: 173
Location: Lancaster, PA
I'll have to take some pictures tomorrow for you.

Well, the capacitors you linked me to are much cheaper than the TVA Atoms anyways. To replace just one preamp board was going to cost almost $20! I don't need the absolute best of the best, but I do want something reliable in it as I plan to use it daily. Not super loud or anything, but I do run my computer into it to listen to music, play games, watch some TV. And I do fire up the turntable on the weekends, if I could narrow down the preamp issue for Phono end of things it would be perfect.


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 9:13 am 
Member

Joined: Jun Fri 22, 2007 12:54 am
Posts: 889
Location: San Diego
We do pretty well with Nichicon, Panasonic, and Vishay/Sprague -- all ordered from Mouser. Digi-Key is also a great vendor.

We use 105 degree caps rather than 85 degree ones.

It is generally not necessary to replace film caps unless they are exposed to high voltages. Put differently, it is much less necessary on solid-state gear than on tube gear.

Do not buy surplus electrolytics. Whereas film caps don't have a significant shelf life, electrolytics do.

Get a can of Caig DeoxIT D5. This is the best contact/control cleaner on the market.

The .17mv spec cannot be correct. Only laboratory-grade meters can measure that small a voltage. The general rule is that you want to set the bias so that approximately 25mA of current flows through the output transistors. Across a half-ohm resistor, for example, that would measure 12.5mV.

Watch out for thermal creep. You can measure this my monitoring the voltage across the emitter resistor(s) or by using an infrared digital thermometer.

Good luck!

Fred
owner
Classic Audio Repair

_________________
www.repairaudio.com


Top
 Profile  
 
 Post subject: Re: HH Scott LK-60 Calibration
PostPosted: Apr Fri 26, 2013 9:28 am 
Member
User avatar

Joined: May Tue 22, 2012 9:58 am
Posts: 544
Location: Hawaii, 96712
Thanks for chiming in, Fred!


Top
 Profile  
 
Post New Topic Post Reply  [ 55 posts ]  Go to page 1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests



Search for:
Jump to:  




















Privacy Policy :: Powered by phpBB