What variation of Scott LK-72 do I have?

[bobinaz]

Started a new thread with the correct model amp in the title. I got this amp recently and am trying to figure out exactly what I have. Some pics I have seen of the lk-72 and lk-72b don't look exactly like mine. So pics are always good.

 

[jkaley]

It's a LK-72-B, the kit version of the 299D. They must have shipped it with a faceplate that was just available when it was new, or the faceplate has been replaced at some point. Use the Scott 299D schematic.

 

[Dave451]

There is an LK-72B schematic in the AK database at:

http://akdatabase.org/AKview/albums/userpics/10007/HH Scott LK-72B Schematic D-LK72B-C1 Sub 0.pdf

Nice amp. The bias adjust uses the same, rather strange method as the LK-48B. There are RCA jacks on top of the chassis to route to the audio input and a switch that you click back and forth and adjust bias for the lowest audio level of the clicking when you work the switch by the topside jacks. I had an LK-48B that used this method and it works, but I didn't like it much. I would rather adjust bias by measuring voltage at the test points shown on the schematic across the 3.3 ohm cathode resistor for each pair and determining cathode current by ohms law.

 

[rickiroo]

It's a LK-72-B, the kit version of the 299D. They must have shipped it with a faceplate that was just available when it was new, or the faceplate has been replaced at some point. Use the Scott 299D schematic.

The later LK-72's came with the gold face plates. Only the early ones were chocolate.
http://hhscott.com/amplifie.htm

 

[btmacdou]

The later LK-72's came with the gold face plates. Only the early ones were chocolate.
http://hhscott.com/amplifie.htm

Not true... with a few exceptions, most brown faced Scotts were sold as kits. Most gold faced units were factory built. Nothing to do with early or late....

And unfortunately the website above has been taken down.

 

[Pablodeux]

Not true... with a few exceptions, most brown faced Scotts were sold as kits. Most gold faced units were factory built. Nothing to do with early or late....

And unfortunately the website above has been taken down.

It's my understanding that all LK72's were all sold as kits, either LK72 or LK72B.
When Scott amplifiers using the 7591 power tubes were sold as factory built amps, they were identified as model 299C, 299D, and 233.

The early LK72's closely resembled the 299C factory built units, although there were numerous running changes to the 299C's that don't seem to have been included in the LK 72 kits.
I've only seen two versions of the LK72's.
Early versions had no Potentiometers to adjust bias Level or Balance for the power tubes, and had only one 20Watt "chalk" resistor mounted on top of the chassis to drop the B+.
The later version had two chalk resistors on top of the chassis, and also had Potentiometers to balance bias current between pairs of power tubes.
I've seen both Brown and Gold face plate versions of the LK72's.

The later LK72's were identified as LK72B's.
The schematics for the LK72B's were identical to the factory built version 299D (Below S/N 249780).
The LK 72B's had Potentiometers to adjust both bias current Level and Balance, and three "chalk" resistors mounted on top of the chassis.

The later (final) versions of the 299D and all 233's were factory built, had three Electrolytic Can caps, and slightly smaller output transformers.
These were all factory built and came only with Gold faceplates.

There was a Scott 7591 amplifier sold in console cabinets with no face plate at all identified as a model 208.
The consoles had a turntable and might have also had a Tuner.
There was also a family of Receivers with 7591 output tubes identified as model 340.

 

[btmacdou]

Scott did offer both kit and wired versions of the LK-72 as far back as 1961. Check out this evidence:

• Attached PDF which is a print from the original HHScott.com website which is now dead. That site was a plethora of excellent information and was created and curated by Lee Schuster, an HH Scott expert who I know personally. Lee is still kicking as of this writing, but he gave up managing the HHComm site to spend more time with family. Anyway, in this document from the HHScott.com "Instabase", Lee shows prices for both wired and kit versions of these amps.
• Also attached, link to an excellent document by Daev Rohr, another Scott expert and long time friend of Lee Schuster. I've also known Daev for many years. Daev compiled a document describing the known versions of the HH Scott catalogs, and includes photos of price lists showing both Wired and Kit versions!

https://farmedia.com/wp-content/uploads/2020/06/HH-Scott-Catalog-doc-list-2020.pdf

​

​

Note that the catalog document suggests that the LK-72B was perhaps only offered as a kit. It also suggests that kits started out as brown face but were offered with gold faceplates later.

Also, I know that there are at least 3 different schematic versions of the LK72 (including the LK-72B), and there is a hint that a 4th (Sub 2) also exists, though I could not find one:

1. Schematic D-LK-72-C1 Sub 1: LK-72 with no balance or bias pots. Schematic for this version is on AK Database only as far as I can tell
2. Schematic D-LK-72-C1 Sub 2: ?? Assume this exists but have not found one
3. Schematic D-LK-72-C1 Sub 3: LK-72 with balance pots only. Schematics for this version are all over the net.
4. Schematic D-LK-72B-C1 Sub 0: LK-72B with both Balance and Bias pots

 

[Pablodeux]

Scott did offer both kit and wired versions of the LK-72 as far back as 1961. Check out this evidence:

• Attached PDF which is a print from the original HHScott.com website which is now dead. That site was a plethora of excellent information and was created and curated by Lee Schuster, an HH Scott expert who I know personally. Lee is still kicking as of this writing, but he gave up managing the HHComm site to spend more time with family. Anyway, in this document from the HHScott.com "Instabase", Lee shows prices for both wired and kit versions of these amps.
• Also attached, link to an excellent document by Daev Rohr, another Scott expert and long time friend of Lee Schuster. I've also known Daev for many years. Daev compiled a document describing the known versions of the HH Scott catalogs, and includes photos of price lists showing both Wired and Kit versions!

https://farmedia.com/wp-content/uploads/2020/06/HH-Scott-Catalog-doc-list-2020.pdf

​

View attachment 3177902​

​

Note that the catalog document suggests that the LK-72B was perhaps only offered as a kit. It also suggests that kits started out as brown face but were offered with gold faceplates later.

Also, I know that there are at least 3 different schematic versions of the LK72 (including the LK-72B), and there is a hint that a 4th (Sub 2) also exists, though I could not find one:

1. Schematic D-LK-72-C1 Sub 1: LK-72 with no balance or bias pots. Schematic for this version is on AK Database only as far as I can tell
2. Schematic D-LK-72-C1 Sub 2: ?? Assume this exists but have not found one
3. Schematic D-LK-72-C1 Sub 3: LK-72 with balance pots only. Schematics for this version are all over the net.
4. Schematic D-LK-72B-C1 Sub 0: LK-72B with both Balance and Bias pots

Your attached catalog page sure does seem to indicate there was such a thing as wired LK 72 and identified it as an LK72W.

I'm guessing this would have predated the early 299C models, since it wouldn't have made much sense to offer both products that were identical at the same time.