In this new series, I walk through the process of repairing a Heathkit AA-100 stereo amplifier. This was called "Unrepairable" by 3 technicians. Can we make it run?
Nice amp with decent iron in it. You could do a version of your PCB that would replace the 7199s with 6GH8/6U8 types, which are cheaper and much easier to get. Adapters are also available. I think that RCA was screwing around with the tube market when they made the pinout unnecessarily incompatible with other similar tubes (they were experts at this). A number of years ago I removed the heat-damaged power amp PCB from an AA-100 (bias supply), replacing it with a subchassis employing turret strips. At that time, there were no eastern European 7591 tubes available and NOS ones were impossible to find. There are two other tubes having different bases but identical characteristics: 6GM5 (standard 9-pin base) and 7868 (Novar 9-pin base). As 7868 tubes were used by Ampeg in some of their guitar amps and getting pricey as a result, I put 9-pin sockets on my subchassis to use 6GM5s. This worked well. I wonder how many 7591 tubes have been destroyed in amplifiers due to selenium diodes deteriorating in the bias supply?
Nice Hickok 752A you've got there. I have a bunch of Hickok testers but the 752A is my favorite, my go-to tester 99% of the time. These were built up into the mid 1970s and yours is slightly later than mine because-mine has the older-style bakelite-housing meter and yours has a more modern, low-profile plastic meter. These were once the reference tube checker for the Federal Aviation Administration, and will test nearly any tube from the 1920s right up to the end of the tube era (with the exception of obscure antique European tubes, big transmitting tubes and some Western Electric types for which setup data was never printed), assuming of course that you have the setup data for the tube in question, or are able to figure out how to set it up using the data provided in a tube manual. Excellent units, and I really like the fact that you can test the 2nd half of a dual triode such as a 12AX7 simply by pushing the Plate 2 button. (Although the owner's manual doesn't tell you this you can even test the 2nd half of a rectifier tube by pushing the plate 2 button, and the only other thing you will have to change is the shunt knob setting for the second diode half of the rectifier). I also owned the earlier model 752 before I got the A version (the A version includes sockets for 9 pin Novar tubes such as the 7868, and 12 pin Compactron tubes), and I am very familiar with these units, so if you have any questions feel free to ask. I have an entire overstuffed loose-leaf ring binder of setup data for obsolete tubes and European tubes and even several photocopied roll charts from different years!
It has been a rock solid unit since I got it. This one came out of a radio station. It had been gathering dust in a store room for years. You know the story....."it's too good to throw out but I have no use for it." They were glad to have me take it away!
@@daystromaudio1903, nice snag! My first 752 cost me $40 at a flea market some 25 years ago. I paid more than that ---- $60 ---- for copies of an owner's manual and all the test data for foreign and obsolete tubes etc. Eventually I sold it and bought a 752A on ebay (about $400, some 15 years ago) so I wouldn't need to use separate adaptors for testing Novars, Compactrons and the like (I used to sell tubes online and being able to test anything and everything with one unit is very convenient; I also work for an audio repair shop and was testing Nuvistors for a McIntosh preamp recently). I think they sell for around $1k these days, yikes!
I have one of these in the garage. Not sure if it still works or not, but I'm going to find out and if necessary repair and recap it. Also have a nib un-assembled AA21 and matching tuner I am about to build.
That's amazing to come across unbuilt kits like those you have. You will have a good time putting them together! Regarding the AA-100, the power output PCB is often fried from the heat of the tubes. I sell a drop-in replacement for these which uses the same circuit design but with fresh components and it also has independent bias controls for the output tubes. Check out these links for more information. aa100restoration.wordpress.com/ www.ebay.com/itm/333954566862
The EF86 is also known as the 6267, and ( more rarely) as the Z729. All have the same pinout and are interchangeable in most circuits. Unfortunately they are also known for being microphonic which is a major problem for some Vox guitar amplifiers that use them. The 5879 tube (often found being used as a mic preamp tube in commercial paging amplifiers) is somewhat similar but has lower gain and *a different pin-out*, therefore it's not a drop-in replacement. The 6AU6 (7-pin pentode) also has some similar characteristics but once again is far from being a drop-in replacement due to requiring a different socket.
this is nice "how to test tubes" segment, but where is "repair pt2, pt3..." Never got fixed? I also had a dickens of a time finding replacement cap cans for the power circuit.
I was wondering when somebody would ask! ;-) Life got in the way, then I started to get repair/restoration work. When there's a break in the action, I'll throw it back on the bench and start working at it again.
@@daystromaudio1903 Excellent. Ya know, you could make some extra money if you sold an update kit like the power section; power cap cans, etc. I see you had a similar kit sent to you in one of your other episodes. That is gold!
Gee, do you think the cosmetics of this unit were designed by somebody who formerly worked in Detroit, for GM or Chrysler perhaps? I seem to recall some old Grommes equipment that had similar car- dashboard cosmetics.....
@@daystromaudio1903 Possible to buy it as a bare board or design files and a bom? I live in sweden so the shipping usally gets to be too much from the US and I really would like to assemble the board myself anyway. I have the original schematic for the amp. I really would lik to build it as mono blocks though.
Nice amp with decent iron in it.
You could do a version of your PCB that would replace the 7199s with 6GH8/6U8 types, which are cheaper and much easier to get. Adapters are also available. I think that RCA was screwing around with the tube market when they made the pinout unnecessarily incompatible with other similar tubes (they were experts at this).
A number of years ago I removed the heat-damaged power amp PCB from an AA-100 (bias supply), replacing it with a subchassis employing turret strips. At that time, there were no eastern European 7591 tubes available and NOS ones were impossible to find. There are two other tubes having different bases but identical characteristics: 6GM5 (standard 9-pin base) and 7868 (Novar 9-pin base). As 7868 tubes were used by Ampeg in some of their guitar amps and getting pricey as a result, I put 9-pin sockets on my subchassis to use 6GM5s. This worked well.
I wonder how many 7591 tubes have been destroyed in amplifiers due to selenium diodes deteriorating in the bias supply?
The kits don't sell fast enough to justify a re-design.
Nice Hickok 752A you've got there. I have a bunch of Hickok testers but the 752A is my favorite, my go-to tester 99% of the time. These were built up into the mid 1970s and yours is slightly later than mine because-mine has the older-style bakelite-housing meter and yours has a more modern, low-profile plastic meter. These were once the reference tube checker for the Federal Aviation Administration, and will test nearly any tube from the 1920s right up to the end of the tube era (with the exception of obscure antique European tubes, big transmitting tubes and some Western Electric types for which setup data was never printed), assuming of course that you have the setup data for the tube in question, or are able to figure out how to set it up using the data provided in a tube manual. Excellent units, and I really like the fact that you can test the 2nd half of a dual triode such as a 12AX7 simply by pushing the Plate 2 button. (Although the owner's manual doesn't tell you this you can even test the 2nd half of a rectifier tube by pushing the plate 2 button, and the only other thing you will have to change is the shunt knob setting for the second diode half of the rectifier).
I also owned the earlier model 752 before I got the A version (the A version includes sockets for 9 pin Novar tubes such as the 7868, and 12 pin Compactron tubes), and I am very familiar with these units, so if you have any questions feel free to ask. I have an entire overstuffed loose-leaf ring binder of setup data for obsolete tubes and European tubes and even several photocopied roll charts from different years!
It has been a rock solid unit since I got it. This one came out of a radio station. It had been gathering dust in a store room for years. You know the story....."it's too good to throw out but I have no use for it." They were glad to have me take it away!
@@daystromaudio1903, nice snag! My first 752 cost me $40 at a flea market some 25 years ago. I paid more than that ---- $60 ---- for copies of an owner's manual and all the test data for foreign and obsolete tubes etc. Eventually I sold it and bought a 752A on ebay (about $400, some 15 years ago) so I wouldn't need to use separate adaptors for testing Novars, Compactrons and the like (I used to sell tubes online and being able to test anything and everything with one unit is very convenient; I also work for an audio repair shop and was testing Nuvistors for a McIntosh preamp recently). I think they sell for around $1k these days, yikes!
I have one of these in the garage. Not sure if it still works or not, but I'm going to find out and if necessary repair and recap it. Also have a nib un-assembled AA21 and matching tuner I am about to build.
That's amazing to come across unbuilt kits like those you have. You will have a good time putting them together!
Regarding the AA-100, the power output PCB is often fried from the heat of the tubes. I sell a drop-in replacement for these which uses the same circuit design but with fresh components and it also has independent bias controls for the output tubes. Check out these links for more information.
aa100restoration.wordpress.com/
www.ebay.com/itm/333954566862
@@daystromaudio1903 Sounds good. Thanks!
The EF86 is also known as the 6267, and ( more rarely) as the Z729. All have the same pinout and are interchangeable in most circuits. Unfortunately they are also known for being microphonic which is a major problem for some Vox guitar amplifiers that use them. The 5879 tube (often found being used as a mic preamp tube in commercial paging amplifiers) is somewhat similar but has lower gain and *a different pin-out*, therefore it's not a drop-in replacement. The 6AU6 (7-pin pentode) also has some similar characteristics but once again is far from being a drop-in replacement due to requiring a different socket.
I always thought it was cool to hear the echo from thumping the tube! ;-)
this is nice "how to test tubes" segment, but where is "repair pt2, pt3..." Never got fixed? I also had a dickens of a time finding replacement cap cans for the power circuit.
I was wondering when somebody would ask! ;-) Life got in the way, then I started to get repair/restoration work. When there's a break in the action, I'll throw it back on the bench and start working at it again.
@@daystromaudio1903 Excellent. Ya know, you could make some extra money if you sold an update kit like the power section; power cap cans, etc. I see you had a similar kit sent to you in one of your other episodes. That is gold!
Gee, do you think the cosmetics of this unit were designed by somebody who formerly worked in Detroit, for GM or Chrysler perhaps? I seem to recall some old Grommes equipment that had similar car- dashboard cosmetics.....
I've often wondered the same thing.
Do you have a website? I could only find your pcb on Ebay.
The website wasn't getting any traffic for a long time so we turned it loose. Our ebay store is the only way to buy the pcb these days.
@@daystromaudio1903 Possible to buy it as a bare board or design files and a bom? I live in sweden so the shipping usally gets to be too much from the US and I really would like to assemble the board myself anyway. I have the original schematic for the amp. I really would lik to build it as mono blocks though.
@@rimmersbryggeri All of the circuit boards have been built up into kits so there are no bare boards available.