I was on a real vintage audiophile kick in the late oughties; I think I owned an example of every style of speaker for a while, and many different amplifiers, preamp, turntables, and a whole bunch of other things. It was fun while it lasted, but interests change. I’ve cut down to a single Harmon Kardon amp, a U-Turn turntable and a good set of Sennheiser headphones. I spend my money now on finding good deals on vintage vinyl.
I wrote up a couple of my restorations through the AudioKarma forums. From time to time, I still get questions about that work. Before that work disappears to the digital sands of time, I am going to move over a couple of the better threads here. Enjoy!
The H.H. Scott LK-60 was an early solid-state integrated amplifer kit based on the H.H. Scott 260. I got these for free, off my local Freecycle. Not one, but two of these beauties, one with a tone circuit issue, the other an incomplete parts unit. Both were in wood cases, nice looking front panels and knobs, and the complete assembly manuals with all the paperwork (included receipts and warranty cards). All this was given away by the original builder.
The photos, as blurry as they are, cheat a little. I’ve cleaned the front panel and knobs, and refinished the case. But since I’ve yet to spend money on stuff for it, it’s still free…right?
The LK-60 is essentially the kit form of the H.H. Scott 260 – they appear to be the same, right down to the boards used. As a kit the work is a bit easier than a Heathkit; these boards were pressembled and tested – “”All”” the kit-builder had to do was solder the wires and chassis components, and do a bunch of mechanical assembly. They had to be adept at wielding a soldering iron since all the wiring was PVC which melts and shinks with any application of heat.
I start my restorations with a cleaning up of the outside. If I don’t see that it will look pretty enough to have in my living room, why bother doing anything else? The front panel took some babying – the panel lettering is fragile and only silkscreened on – so no hard scrubbing or you’ll lose them. The thin finish on the veneer wood case (I got two in this deal) needed some attention. I cleaned it up with Minwax Antique Furniture Refinisher and then applied several layers of Walnut Danish Oil with light sandings in between. The aluminum grille had a yellowed layer of laquer that I quickly removed with hot water and degreaser.
(ed.: the knobs took the most attention. the brass caps were dull and were barely hanging on to the plastic. I’ll write up the process on how I recovered those another time)
I like my electronic restoration to look like it belongs, especially when somebody can see inside. There are a large number of electrolytic caps to replace in this amplifier, and radials will not do. I could not find an axial capacitor series that would fit all of the values without selecting far larger voltage rating, and while the old caps were big, they weren’t that big. I bucked the conventional wisdom of using the best Panasonic or Nichicon radials I could find, and selected the axial Sprague TVA Atom series.
Why, Dave, why? I hear the scoffing. ‘They have substandard audio performance’ (whatever that means). Lower lifetime ratings. They are not Japanese. OK, here is my logic.
One: Atoms are still better than the original capacitors from back in the early 60’s. We have the benefit of decades of capacitor design and process control and automation, resulting in a far more consistent and higher performance part.
Two: The theory of better caps making an entire audio device better sounding smacks of magical belief. If I put in capacitors of similar design into this amplifier, I ‘should’ get similar performance to that originally designed and approved by the engineers who designed this.Which seemed good enough for this to be considered a fairly decent amplifier back then.
Three: Axials are going to look WAY nicer on these PCBs, and will exactly match the original component values. Making that decision made the work easy, since they fit very nicely and you can get old-fashioned values (5uF, 50uF, those wonderful old round numbers).
I will tell you that with capacitors, most of my time was spent finding the perfect output capacitor. If you are concerned about the quality of the part affecting performance, that’s the first part to consider. I spent a lot of time finding the perfect cap with for screw terminal and the same outer diameter, so they could drop right in. Large crimp terminals made the reattachment easy.
My restoration process:
Remove bottom cover, preamp circuit cover, front panel, knobs, panel meter, fuses
Get your iron hot, and then let’s remove each of the circuit boards.
QUICKLY heat the joint between the wire and PCB terminal point, and pull up on the wire(s). You want to do this quick since the wire insulation is PVC and will melt/shrink when hot. Keep the wire in about the same area of the chassis, this helps later. Once you have freed a PCB of all the wires connected to it, remove the four screws (two screws for the preamp board) and lift the board away. Repeat five more times; don’t worry, the boards are exactly the same between the right and left sides.
One by one, clip away the old capacitors. You may take notes of position and orientation; this is already in the manual on the back of the schematic page. Working fast and deliberately, use the wick to remove the solder and remaining leads. Clear as much as the solder as you can from the terminal points without heating the board too much – this is where you want good soldering skills – the better you clean the points the easier it is to reassemble, but if you heat the joint too long you will delaminate the attached trace from the board.
If your board has socketed transistors, remove them but take careful note of their position on the board; on the driver board the same transistors are used but they seem to have sorted them in some way. It’d be best to try and maintain the positions of those parts. Now pour alcohol into a bowl/basin, and using a small paintbrush, delicately scrub the top and bottom sides with the alcohol (about 30-45 seconds) over a sink. Then dip the board in the alcohol for a final rinse for 10 seconds, then holding the board firmly, flick it dry. I have sometimes used a water rinse, but I usually follow it with a bake in a warming oven. This absurd amount of work removed dust, flux residue, oils, and will leave you with a clean good-as-new board. If you are doing the driver board with the two pots, use compressed air (or the can-type ‘duster’) to blow out the alcohol/water, then follow with Deoxit/FaderLube to replace the lost lubricants.
At this point I took the time to measure all of the resistors on the boards and chassis. The general rule is that you should never see a resistance HIGHER then the nominal+tolerance of the resistor, sometimes within, and sometimes lower. As you have removed/disconnected alot of stuff, you are going to find that most resistances are within their 10% tolerance. For the low ones, go back and desolder, lift one side out of the board. You should be able to measure the resistance without the influence of other parts once you do this. I found that there is a minor resistance change on the preamp boards not documented in the schematic. If somebody is interested, I’ll find it. Replace any out-of-tolerance resistors with 1/2W carbon-film types or carbon comp if you can get them new (no NOS).
Now to replace the capacitors. Estimate the points to bend, and bend with your needle nose pliers. I can tell you now that none of the capacitors get bent right at the body, there will be the need for at least a little lead on each end. Insert, bend the leads long the path of the PCB trace, and cut with your diagonal pliers such that you have about 1/8″ laying on the trace leading to the pad. Solder. Over and over again! Once you’ve finished, inspect your work, checking for joints you forgot to solder, incorrect polarization or component values, or any other damage. Repair as required.
You might think – hey, how are you going to wire all that back up? So many connections! As this was a kit using prebuilt boards, all the instruction manual describes as how/which color wire goes where. My manual is my notes!
One by one, reinstall each board. Clip a short section of heat shrink and slip over the wires. Bend the end into a squareish loop, and press into the slot of each board terminal. Along the way think about how the wires are sitting on the chassis, and rearrange the wires for nice clean and orderly runs. Don’t solder yet, until you know that no more wires are going into the slot – Scott broke up the wiring for all but the preamp board into multiple sections. Once you have all the wires in place for a board, recheck the drawings, then solder. Slip down the heatshrink (because the PVC shrinks, don’t it?) and use a heat gun to complete the operation.
Do a final check of the wiring, looking for forgotten connections, wrong connections, burned insulation, etc. Repair.
Remember the mechanical/electrical parts you removed? Put them back in, in the same order/location you took them out of. At this time, if you’d like to replace the old clear thermal compound with white thermal compound, now is a good time. Take care to remember the orientation of the QA-10 transistors in the heatsink. If you want to do the same for the 2N3055, It only takes two screws on the underside of the chassis to loosen each heatsink block for access and two more on each transistor.
Put the front panel, meter, knobs back on. Good tools prevents damage.
Everything back together? Again, go over the whole thing, comparing it to manual photos and other photos…then do the Initial Test as described in the manual. This is a neat kit – they have an ‘INITIAL TEST’ position to allow you to determine if you dead-shorting something without destroying the amp. It passed in the first go.
If that goes well, do the balance and bias procedure, and if that goes well, stick in some headphones, connect an iPod or hat have you to the extra input, and try things out. Run it for a long duration at low power, shake/poke/turn to try things out. I had an issue with weak audio on one side – but with a little debugging, the problem is resolved, and glorious, rich sound is coming from the KLH 24s I’ve hooked up to them. I ran the detailed test procedure in the manual, buttoned it up and I’m done! Another classic restored.
I liked this restoration so much, I got the matching LT-112B FM Tuner and restored that. They look nice together, eh?
All Parts from Mouser Electronics
Chassis Components (first section caps, second is optional stuff)
(2) 539-CGS222075R2C 2200uF 75V Screw Terminal Capacitor
(1) 75-36DY102F100AN2A 1000uF 100V Screw Terminal Capacitor
(1) 594-2222-021-19102 1000uF 100V Axial Capacitor
(1) 75-TVA1312 250uF 50V TVA Atom Axial Capacitor
(2) 844-1N1206A 600V 12A stud-mount rectifier
(1) 863-1N5361BG 27V 5W Zener Diode
(1) 606-CM1819 #1819 Lamp
(2) 581-5OQ472KOHAM 0.0047 uF ceramic capacitor (one extra inc.)
(1) 30BJ500-39K 39KOhm 1/2W resistor
Ring Lugs from personal stock
Driver Boards (both inc.)
(2) 75-TVA1414 50uF 150V axial
(4) 75-TVA1161 250uF 16V axial
(2) 75-TVA1206 50uF 25V axial
(2) 75-TVA1306 25uF 50V axial
Tone Boards (both inc.)
(2) 75-TVA1160 100uF 16V axial
(4) 75-TVA1306 25uF 50V axial
(4) 75-TVA1204 10uF 25V axial
(2) 75-TVA1301 2uF 50V axial
Preamp Boards (both inc.)
(2) 75-TVA1161 250uF 16V axial
(4) 75-TVA1204 10uF 25V axial
(2) 75-TVA1206 50uF 25V axial
(2) 75-TVA1303 5uF 50V axial
(2) 75-TVA1301 2uF 50V axial