across the bench: an electronic menagerie of diagnostic oddities plus photos and design analysis

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toshiba 2sa1943 part number, if only they had positioned one output above the pcb and the next one under the pcb that would have given the high power outputs some breathing room. instead of stepping on each others thermal toes.

with all five channels running at moderate movie output level, i wonder how much of a hot spot is created inside the chassis.

https://toshiba.semicon-storage.com/info/2SA1943_datasheet_en_20160107.pdf?did=20427&prodName=2SA1943

*230v 150w rated pnp

 

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decent ventilation under the chassis so doing an under-board recap should help with thermal longevity.

 

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slowly dialing in the bias and evaluating stability vs thermal drift

the amp had one channel blown fuse and a different channel had its primary wire harness disconnected. channels one and five were affected. installed new fuse and reconnected the other channel, also set bias to minimum on all channels before startup. usual dim bulb and variac slow&low procedure.

everything seems fine, no major repairs needed so far but a recap would be something to consider plus strategic use of film caps. overall a capable amp with some enhancement potential. tantalum cap on the fuse pcb should also be updated to something less explosive.

 

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interesting little receiver that sounds better than it should, looks like it had a recap... and one cap only it would seem, what is up with that. cooker power resistor on a pcb full of electrolytics surrounding it, the usual design.

 

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realistic sta-78 stereo receiver, slightly aged and yet still functional

 

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https://akdatabase.org/AKview/albums/userpics/10007/Realistic%20STA-78%20Service%20Manual.pdf

*locally sourced, free range, digitally organic service manual.

Realistic STA-78 Repair and Rebuild!

Greetings people of AK. Today i got a Realistic STA-78 from another buddy of mine that he wants fixed. He described the issue to me as loud pops and cracks when using the Phono input. i got it on the bench and quickly found that all the controls were dirty. cleaned them and all seemed good...

audiokarma.org

STA-78 Cat. No.= 31-2077 Radio Radio Shack Tandy, Realistic, Micronta |Radiomuseum.org

STA-78 Cat. No.= 31-2077 Radio Radio Shack Tandy, Realistic, Micronta; USA, build 1978/1979, 2 pictures, United States of America , schematics, tubes

www.radiomuseum.org

 

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Complete List Of All Realistic and Optimus Stereo Receivers

I have always been fascinated with vintage and modern electronics and especially audio and video equipment. Lately I have been bit by ...

justoldstuff.blogspot.com

*hour scroll memory lane

1986 Radio Shack Catalog

Flip through the 1986 Radio Shack electronics catalog containing: vintage hi-fi stereos, radios, recording devices, headphones, computers, CBs, electronic components, test equipment, electronic kits & more!

www.radioshackcatalogs.com

*one comment from above link pointed to this

1978 Radio Shack Catalog

Flip through the 1978 Radio Shack catalog containing vintage: radios, stereo systems, tape players, CB radios, walkie-talkies, scanners, headphones, telephones, electronics, test equipment & more!

www.radioshackcatalogs.com

*page 32 for the 22 watts of terror per channel

lots of content for those whole remember paging through radio shack advert catalogs. great way to kill a few hours/days especially when escaping the in-laws during the holidays. oops, i said the quiet part out loud, naughty me... hello lump of coal, lots of diamond potential.

 

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available nov 30, 1977

 

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going one step further:

Inflation Calculator | Find US Dollar's Value From 1913-2025

Easily calculate how the buying power of the U.S. dollar has changed from 1913 to 2025. Get inflation rates and U.S. inflation news.

www.usinflationcalculator.com

for those who enjoy apples-to-apples numerical comparisons of expensive audio gear, regardless of what year today is. numbers might be different after 18dec25 as noted in the screenshot above.

 

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fairly clean inside. the upgraded solo cap is on the square board below the mains txf, cap below the parallel fuses.

something to note is the large red power resistor that heat soaks the pcb quickly on the same fuse board.

 

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moderate amount of wire harness activity bundled underneath

 

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reasonable idle wattage but a recap would still be recommended plus some thermal longevity modz

 

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yet another conrad johnson pv-5 that needs a major overhaul (even low hours systems). also a bryston 4b power amp getting ready for inspection, analysis, recap and maybe some enhancements.

 

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a new mod for the bench. hungry filament bulb with XL vintage glassware appeal. using a step down txf from a mirage plate amp to dial down the normal 60w to something more decorative (variac helps too). could also use this monster sized decoration with the dim bulb tester, hmm thats an idea.

60W Replacement PS52 E26 Dimmable Amber Glass Vintage Edison Incandesc

Turn home lighting into an expression with the beautiful glow of Original Vintage filament light bulbs. These Filament Light Bulbs are made with exposed filament and wrapped in a glass housing to deliver an elegant traditional look and feel.

www.feit.com

 

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a somewhat normal pv-5/pv5 with multiple rodent contributions since this must have been stored in a barn for a few decades. cleaning definitely needed, low mains voltage testing has indicated this system is functional but needs a major rebuild.

 

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Conrad Johnson PV5 All-Tube Preamplifier with Phono

This is a super capable all-tube preamplifier from Conrad Johnson. Fully tested in our shop to clean and quiet controls, good tubes, now ready to rock! This also comes with its rare original box.More from Conrad Johnson: The PV5 was a completely new preamp in all areas. The sophisticated...

skyfiaudio.com

Conrad Johnson, PV-5 Tube Preamp - Classic HiEnd

What to know about the Conrad-Johnson PV5? The sophisticated circuitry allowed the PV5 to outperform preamps nearly three times it price. The PV5 was the personal choice as a reference preamp for many audio reviewers at the time! Low noise mil-spec resistors and polypropylene capacitors were...

holthill.com

not sure if there is some mystical difference with the model labeling pv-5 vs pv5 but it is interesting to note.

 

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mouse nuggets, sawdust and who knows what other substances. looks like a low hours preamp judging by the minimal pcb thermal discolorations.

 

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rectifier area looks decent. one of the two power caps aged into a resistor over time.

 

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slowly rebuilding the preamp and modifying a few things. the new owner is interested in going further with my longevity modz ideas.

the b+ and filament electrolytics were used to get the system up and running while shopping for a better film solution. filament supply uses multi thousand uf although a different direction is possible.

still leaning towards oem txf delete redesign plus improved chassis venting...

a few radical modz in the brain pipeline but they should stay in the hardcore r&d dept until adequately tested/tuned.

 

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using a jj 500v double cap 100uf per. not exactly a high quality/longevity component but it helps to get the system up and running to stress test other parts of the preamp including all bottles.

Capacitor - JJ Electronics, 500V, 100/100µF, Electrolytic | Amplified Parts

Same diameter as LCR. Great for use in Marshall amplifiers. 1-3/8" dia. x 2 7/8" height. S-H122 is a good mounting clamp for this can

www.amplifiedparts.com

cap mounted in a way that makes installing chassis cover impossible, have to go horizontal on this one. oh the horror of having lots of pcb surface area to utilize...

JJ Capacitor 100uF x 100uF / 500V - www.thetubestore.com

Buy the JJ Can Capacitor 100uF x 100uF / 500V online. They are in stock and ready to ship! Upgrade the caps in your tube amplifier for better tone.

www.thetubestore.com

https://www.thetubestore.com/lib/thetubestore/JJ-caps.pdf