Just finished EJ Kozette XAM (HK A300)

[kevintaft]

Just finished my XAM from EJ Kozette, a HK A300 hiding in Plain Jane clothes. Fortunately it was functional when i got so i was able to test the precondition vs the final config. Average output power before distortion about 10 to 11 watts per channel . Not bad given the Iron that the A300 comes with. First step replace all the electrolytics with brand new which increased output tube biasing voltages by about 6 volts, reduced hum and fixed low preamp voltage to published specs. Next was to test the 6V6 and 7408 tubes it was designed for, on my emission tester they tested in the upper 80% range. Wait, the pin out of the 6V6 is similar to the 6L6 only major difference is the filament requirements being about twice that of a 6V6. First Mod, install a new 6 amp filament supply. After testing the 6L6 in place of the 6V6 I neglected to account for increased plate current which caused the cathodes to ride at about 30+ volts. HK engineers used the preamp tubes filaments as the output tube cathodes DC supply so i was driving the pre amps kinda hard, 2nd mod: next came a switch to change bias so that 6V6 run at about 24 volts and the 6L6 run at about 30 volts but keep the preamp filaments at a cool 23.5 volts (50 ohm resistor and 3 amp diode) now i can run both 6V6/7408 and 6L6. Check output watts using the 6L6 and they increased to well over 15 watts per channel. Next step replace all couplers, none had failed but most had varied in tolerance. Vitamin Q Del Ritmo for output tubes, and Toichi Vit Q for phono preamp including some Orange drops to complete the restoration. Final output power per channel at about 18 watts per channel before distortion. Running New Issue Mullard 6L6 in the output. Some minor cleaning, deoxit and polishing and this is the final condition. Kevin

 

[knockbill]

That's cool,,, looks just like HK gear,,, EJ Korvette was a discount chain after WW2,,, if that's the store you meant...

 

[larryderouin]

Kinda like a poor mans Walmart. They competed with K-Mart, and Woolworths for customers.

 

[airtime]

I had a EJ Korvettes up the block from my house. It was NOT the poor mans Walmart. Actually their audio and record departments were exceptional with mpst major brands being sold there. Not only did they have the TOTL of those brands but I also remember they had a few of the more high end tube products.

And their sports department was great. That was back in the day when a kid would drool over a baseball mitt and football helmet. Their camera and telescope section was pretty well stocked. That was the first time I EVER saw an 8" telescope.

EJ Korvette's catered to the full middle class. Some good stuff, some cheap stuff and a touch of high end. I miss those simple days.

 

[kvflyer]

I had a EJ Korvettes up the block from my house. It was NOT the poor mans Walmart. Actually their audio and record departments were exceptional with mpst major brands being sold there. Not only did they have the TOTL of those brands but I also remember they had a few of the more high end tube products.

And their sports department was great. That was back in the day when a kid would drool over a baseball mite and football helmet. Their camera and telescope section was pretty well stocked. That was the first time I EVER saw an 8" telescope.

EJ Korvette's catered to the full middle class. Some good stuff, some cheap stuff and a touch of high end. I miss those simple days.

For sure, Korvette was an upper middle class store. I worked there from summer 1966 to the end of 1967. I managed to weasel my way into the audio department. Imagine, a teenager, selling all of the high end electronics; Fisher, Harman Kardon, HH Scott, Garrard, Scott-Kit kits etc. It was a dream come true. My first job (until I got drafted). I would rate them even higher than Target.

Just my opinion though. It was a fun place to work.

 

[crispycircuit]

OH Ya, I remember the draft notice hanging over my shoulder, we were old enough to get drafted but not drink.!

 

[kevintaft]

Oops, yes EJ Korvette....

 

[airtime]

OH Ya, I remember the draft notice hanging over my shoulder, we were old enough to get drafted but not drink.!

My best childhood friend and I would run home from high school every day and watch the news from Vietnam. Sitting just waiting for the notice. We both got some "pre notice"??? but the draft ended and we never heard from the draft board again!!!!

And yes we weren't old enough to drink - but the local cops knowing what was coming for us would let us. Sometimes even driving us home and looking the other way with DWIs.

 

[crispycircuit]

+1

 

[FlaCharlie]

After testing the 6L6 in place of the 6V6 I neglected to account for increased plate current which caused the cathodes to ride at about 30+ volts. HK engineers used the preamp tubes filaments as the output tube cathodes DC supply so i was driving the pre amps kinda hard, 2nd mod: next came a switch to change bias so that 6V6 run at about 24 volts and the 6L6 run at about 30 volts but keep the preamp filaments at a cool 23.5 volts (50 ohm resistor and 3 amp diode) now i can run both 6V6/7408 and 6L6.

I'll bypass memory lane since there were no EJ Korvettes around here . . .

About the amp . . . this is a post about the amp, right? . . . Nice work!

I'm having a hard time wrapping my head around some of this, though. Would you happen to have a schematic of the mod that allows the use of either 6V6 or 6L6?

I should dig out a schematic of the stock unit to check but I thought that HK used the resistance of the filaments of a couple of 12AX7s in the phono stage instead of using cathode resistors on the 7408 / 6V6s, or something like that, right? So are you saying that the voltage on the cathode was too high with the 6L6s installed so you had to drop it by putting a 50 ohm resistor (what wattage?) between the 6L6 cathode and the 12AX7 filaments? Where does the 3 amp diode (which type) fit in?

I have, I think, 2 1/2 A-300s and modding one to use 6L6s sounds like it might be an interesting (future) project.

 

[NoTransistors]

We had both Korvettes and Lafayette here in Brooklyn. Some of the early stereo tube stuff from Lafayette is incredible.

 

[Dandy]

Interesting line in the Korvette Wikipedia page:

Of note was E. J. Korvette's venture into the home entertainment business. The retailer established a rather out of context series of high-end audio salons within selected stores. Korvettes went so far as to market its own "XAM" brand of stereo receivers, amplifiers (some manufactured by Roland Electronics of Japan), television sets, and speakers. XAM was rumored to be a tribute to the owner's deceased dog, Max.)​

 

[Dadbar]

Growing up on Long Island, our standard family Friday night was dinner at Howard Johnsons and then shopping at EJ Korvettes. Mom would shop for clothes downstairs and Dad and the kids would go upstairs to shop for records (and hi fi).

 

[airtime]

Interesting line in the Korvette Wikipedia page:

Of note was E. J. Korvette's venture into the home entertainment business. The retailer established a rather out of context series of high-end audio salons within selected stores. Korvettes went so far as to market its own "XAM" brand of stereo receivers, amplifiers (some manufactured by Roland Electronics of Japan), television sets, and speakers. XAM was rumored to be a tribute to the owner's deceased dog, Max.)​

Our EJ Korvette's had one of those salons. there was a sizable audio department and right next to it was a separate room. Filled with some very high end stuff. This was the mid or later 60's and they did still carry a number of tubed stereos.

 

[kvflyer]

Our EJ Korvette's had one of those salons. there was a sizable audio department and right next to it was a separate room. Filled with some very high end stuff. This was the mid or later 60's and they did still carry a number of tubed stereos.

And as a teenager, right out of high school, that is the salon that I worked in at E.J. Korvette. What a "Dream come true"

Sorry to drift OT...