Hi fellow enthusiasts,
a dream came true and I was able to buy a set of 1966-1967 Trio/Kenwood TK-400 early solid state amp and TK-500 SS/tube tuner. Both units came as "defective". Upon opening the amp, the reason became clear for this unit at least: All output devices gone. One channel had both emitter resistors burnt. Many chassis screws gone.
Apart from this no visible damage. So possibly after the magical smoke someone sold the two good devices (or all 4???), Sony 2SD46. Someone (else?) had also veneered over the ventilation slits in the cover... a long time ago though.
I call myself lucky that all the PCBS are in place. Hopefully the pair of rare germanium PNP drivers, 2SB421, is still intact. Did not test anything so far. This amp is a late version of which no schematic is findable on hifiengine; it is quite similar board-code wise to the TK-80U receiver from the same time.
When the TK-400 came out in 1965, it was a full Germanium design with doubled output devices; subsequent iterations saw less and less germaniums, until this version which keeps only the two poweramp drivers Germanium (as in a couple of kenwood amps and receivers even into the 1970s, like e.g. the KR-33L).
so my questions are:
1) what size of screws is used to fix the devices to the heatsink? I tried M2,5 headset screws and they seem to work. They seem to need an insulating tube in order to not touch the heatsink.
2) What size are the smaller chassis screws? M3 seems to big.
3) What size are the screws to fix the bottom cover?
4) Is it a good idea to use NOS RCA N3055 devices as replacements? or too slow? I have also a set of new on semi TO-3s from mouser (MJ21194G) from another project (thank you, @Mooly) and might ultimately use them, but they seem overspec'ed, and I'd love to finally use those 3055s lying around.
As it is a single supply amp (-68V), and the 3055 datasheet says |Vce|: 70 V, maybe a bit tight? But maybe I am not completely understanding the specs here.
Some also say the 3055 sounds bad or is not truly intended for audio use. The venerable Revox A50 used them. The SD46 has a much higher ft though.
thanks for your input!
eschenborn
a dream came true and I was able to buy a set of 1966-1967 Trio/Kenwood TK-400 early solid state amp and TK-500 SS/tube tuner. Both units came as "defective". Upon opening the amp, the reason became clear for this unit at least: All output devices gone. One channel had both emitter resistors burnt. Many chassis screws gone.
Apart from this no visible damage. So possibly after the magical smoke someone sold the two good devices (or all 4???), Sony 2SD46. Someone (else?) had also veneered over the ventilation slits in the cover... a long time ago though.
I call myself lucky that all the PCBS are in place. Hopefully the pair of rare germanium PNP drivers, 2SB421, is still intact. Did not test anything so far. This amp is a late version of which no schematic is findable on hifiengine; it is quite similar board-code wise to the TK-80U receiver from the same time.
When the TK-400 came out in 1965, it was a full Germanium design with doubled output devices; subsequent iterations saw less and less germaniums, until this version which keeps only the two poweramp drivers Germanium (as in a couple of kenwood amps and receivers even into the 1970s, like e.g. the KR-33L).
so my questions are:
1) what size of screws is used to fix the devices to the heatsink? I tried M2,5 headset screws and they seem to work. They seem to need an insulating tube in order to not touch the heatsink.
2) What size are the smaller chassis screws? M3 seems to big.
3) What size are the screws to fix the bottom cover?
4) Is it a good idea to use NOS RCA N3055 devices as replacements? or too slow? I have also a set of new on semi TO-3s from mouser (MJ21194G) from another project (thank you, @Mooly) and might ultimately use them, but they seem overspec'ed, and I'd love to finally use those 3055s lying around.
As it is a single supply amp (-68V), and the 3055 datasheet says |Vce|: 70 V, maybe a bit tight? But maybe I am not completely understanding the specs here.
Some also say the 3055 sounds bad or is not truly intended for audio use. The venerable Revox A50 used them. The SD46 has a much higher ft though.
thanks for your input!
eschenborn
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can't upload the pics for some reason right now, upload button unresponsive. will try later. thanks!
The 2N3055 depends on the letter after the numbers --the E-H-S-U are 100V , its the C&V versions that are 80V.
The 2N3055A is (under) <4.5/9us.
Depending on the manufacturer , I use a German equivalents book -VRT .
My UK book gives -2N3055V as 100V +2N3055-3+ 6/7/8 versions .
Also the 2N3055E gives 2.5MHz --others are 800KHz.
I am talking original here what the Chinese or others rate them at I do not know.
I will let others comment on the 2N3055 subjective sound quality as that subject causes some arguments I have found.
The 2N3055A is (under) <4.5/9us.
Depending on the manufacturer , I use a German equivalents book -VRT .
My UK book gives -2N3055V as 100V +2N3055-3+ 6/7/8 versions .
Also the 2N3055E gives 2.5MHz --others are 800KHz.
I am talking original here what the Chinese or others rate them at I do not know.
I will let others comment on the 2N3055 subjective sound quality as that subject causes some arguments I have found.
Original 2N3055's from the late 1970's had an FT of just 0.2Mhz (200kHz) according my old TD Towers book while the Sony 2SD46 was 10Mhz.
A modern 2N3055 (no letters after it) is stated as being 2.5Mhz according to a data sheet.
So I suspect the answer is that a modern part may well be OK but an old NOS part may not. And as you say, the rail voltage is a bit close for comfort.
The 2N3773 is a possible replacement if you want older parts but nothing lost in trying the MJ21194's.
Also be aware that production processes have changed over the years and forward voltages (turn on voltage) can be noticeably different for newer parts and that can cause issues with bias current setting being out of range on some designs.
A modern 2N3055 (no letters after it) is stated as being 2.5Mhz according to a data sheet.
So I suspect the answer is that a modern part may well be OK but an old NOS part may not. And as you say, the rail voltage is a bit close for comfort.
The 2N3773 is a possible replacement if you want older parts but nothing lost in trying the MJ21194's.
Also be aware that production processes have changed over the years and forward voltages (turn on voltage) can be noticeably different for newer parts and that can cause issues with bias current setting being out of range on some designs.
Thanks, duncan2, and thanks, Mooly! Hoped you'd chime in. I still have a great memory of the repair of that Sony amp (I hear that it has worked flawlessly ever since).
Got it, I'll use the newer devices... and starting everything on the DBT so I can carefully set the bias.
Any ideas about the screw sizes? They are probably US norms, while I find mostly EU norms here. The transistor "thief" could at least have left the mounting hardware in the machine...
Thanks again!
Eschenborn
Got it, I'll use the newer devices... and starting everything on the DBT so I can carefully set the bias.
Any ideas about the screw sizes? They are probably US norms, while I find mostly EU norms here. The transistor "thief" could at least have left the mounting hardware in the machine...
Thanks again!
Eschenborn
TK-400E sequel
Here a little update with some more infos.
The amp is functional again. I found original NOS Toshiba 2SC493 output transistors and mounted them. They are specified in the service manual (as said above, this version of the amp is largely identical electrically with the TK-80U receiver. The pre-amp, tone amp, main amp have the same PCB codes).
I have also a couple of RCA 3055s. After I found in the same service manual that they were suggested as replacements I tested them. I found the sound different than with the SC493s. No idea if that was down to my expectation of the RCA devices having a lower ft.
There was a problem with distortion in the tone-amp. Transistors tested ok. It went away after I had changed the caps of the feedback circuit. Most of the old grey Elna caps where off, so they really needed to be replaced in order to have sound coming out.
The pre-amp (equalizer) is not right yet, there are many resistors (carbon comp) which have grossly drifted, so those need to be replaced.
The sound is typical for these old Kenwoods with the SB471 germanium drivers, very liquid and nice to listen to. Focused, sweet and deep (after some upgrades). The amp should deliver about 30 watts into 8 ohms.
In the next generation, the same innards then went into the TK-88 receiver in the new case design with the fake wood panel part. The slightly later KR-100 receiver (in the same fake wood panel part case but with lever instead of rocker switches) still has the basic amp design, but loses the germanium for silicon drivers.
The screws for the transistor mounting hardware and for some other chassis parts (apart from the bottom cover) are UNC #4-40 x 3/4".
Thanks for your comments before! (One of the pics seems to have been turned upside down by the attachment management system, apologies).
Here a little update with some more infos.
The amp is functional again. I found original NOS Toshiba 2SC493 output transistors and mounted them. They are specified in the service manual (as said above, this version of the amp is largely identical electrically with the TK-80U receiver. The pre-amp, tone amp, main amp have the same PCB codes).
I have also a couple of RCA 3055s. After I found in the same service manual that they were suggested as replacements I tested them. I found the sound different than with the SC493s. No idea if that was down to my expectation of the RCA devices having a lower ft.
There was a problem with distortion in the tone-amp. Transistors tested ok. It went away after I had changed the caps of the feedback circuit. Most of the old grey Elna caps where off, so they really needed to be replaced in order to have sound coming out.
The pre-amp (equalizer) is not right yet, there are many resistors (carbon comp) which have grossly drifted, so those need to be replaced.
The sound is typical for these old Kenwoods with the SB471 germanium drivers, very liquid and nice to listen to. Focused, sweet and deep (after some upgrades). The amp should deliver about 30 watts into 8 ohms.
In the next generation, the same innards then went into the TK-88 receiver in the new case design with the fake wood panel part. The slightly later KR-100 receiver (in the same fake wood panel part case but with lever instead of rocker switches) still has the basic amp design, but loses the germanium for silicon drivers.
The screws for the transistor mounting hardware and for some other chassis parts (apart from the bottom cover) are UNC #4-40 x 3/4".
Thanks for your comments before! (One of the pics seems to have been turned upside down by the attachment management system, apologies).
Attachments
PS
The next one in line is a SONY again, a STR-6065 with seriously burnt channels on the power amp board, three shot (original) SONY 2SD88 outputs, one (wrong but ok) SONY TX-183S output, lots of hacked-in resistors in one channel, burnt resistors in the other, one visibly exploded small signal transistor...
Obviously someone had attempted a repair many decades ago and then after failing let it catch dust in some attic. The amp schematic is rather complicated to my eyes. Lots of proprietary SONY silicon. The good thing about these old Trio-Kenwoods is that they have rather robust and simple set-ups.
I'll proceed, DBT-secured, slowly & systematically, Mooly-style, if I might say so, and when I get stuck, I already promise to open a new thread.
My son some weeks ago told me: You need to find a REALLY shot amp, so you can use the scope once again. Well, that seems to have happened. Might take some time though, as much work waits for me at the moment.
The next one in line is a SONY again, a STR-6065 with seriously burnt channels on the power amp board, three shot (original) SONY 2SD88 outputs, one (wrong but ok) SONY TX-183S output, lots of hacked-in resistors in one channel, burnt resistors in the other, one visibly exploded small signal transistor...
Obviously someone had attempted a repair many decades ago and then after failing let it catch dust in some attic. The amp schematic is rather complicated to my eyes. Lots of proprietary SONY silicon. The good thing about these old Trio-Kenwoods is that they have rather robust and simple set-ups.
I'll proceed, DBT-secured, slowly & systematically, Mooly-style, if I might say so, and when I get stuck, I already promise to open a new thread.
My son some weeks ago told me: You need to find a REALLY shot amp, so you can use the scope once again. Well, that seems to have happened. Might take some time though, as much work waits for me at the moment.
Good work with the Trio 🙂 bThe first amp I ever built used germanium outputs (AD149) and it sounded brilliant to me at the time.
The Sony sounds a bit more of challenge... it will keep you entertained 😉
The Sony sounds a bit more of challenge... it will keep you entertained 😉
Thanks, Mooly!
To me personally, the first – Germanium – generation of solid state has something very seducing in the way many components sound. The first series of the TK-400 is full Germanium, with SB26A outputs. I'd loved to have found that one, but I assume it's only findable in the US.
I'd be curious how your first amp sounded 🙂
And as to that SONY, if it becomes really profoundly entertaining, I'll cry for help. A nice member over at AK has sent me a high-res scan of the service manual, so at least I can see what is going on there.
To me personally, the first – Germanium – generation of solid state has something very seducing in the way many components sound. The first series of the TK-400 is full Germanium, with SB26A outputs. I'd loved to have found that one, but I assume it's only findable in the US.
I'd be curious how your first amp sounded 🙂
And as to that SONY, if it becomes really profoundly entertaining, I'll cry for help. A nice member over at AK has sent me a high-res scan of the service manual, so at least I can see what is going on there.
It sounded very good to me at the time. My parents had a B&O Beocentre3500 and the germanium amp was as good if not better in its musical presentation. It was a relatively simple design, single rail AC coupled and built from a kit. Harversonic 10+10
The power of the internet. This looks like it. Pity there isn't a better view.
The power of the internet. This looks like it. Pity there isn't a better view.
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those look gorgeous! so you constructed one from scratch (wouldn't be surprised) – or built it from that kit?
those remind me of my (presumably) oldest amp, germanium outputs and transformers as phase splitters. after the restoration it sounded fantastic, I'd say really top class. that should be all what I'd actually need.
Here is the link to the SM, it's a Monarch SA-500: https://www.audiovintage.fr/leforum/download/file.php?id=113061)
those remind me of my (presumably) oldest amp, germanium outputs and transformers as phase splitters. after the restoration it sounded fantastic, I'd say really top class. that should be all what I'd actually need.
Here is the link to the SM, it's a Monarch SA-500: https://www.audiovintage.fr/leforum/download/file.php?id=113061)
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It was built from the kit. The power amp was a classic 5 transistor circuit , it certainly sounded terrific. The case was good with a printed brushed aluminium type front panel and it had a wrap around wooden sleeve.
The SONY STR-6065 receiver has been revived, thread here: https://www.diyaudio.com/forums/solid-state/376697-sony-str-6065-repair-restoration.html#post6777631