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

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inside the m-1.0t amp.


chassis might be small but there is a healthy amount of wattage contained within.


december of 88 marked on the txf. also some nelion update boards.

Carver M-1.0t mkII opt002 Restore and Upgrade

A super-charged upgrade and restore for your Carver M-1.0t from Nelion Audio, a Carver authorized, Bob Carver recommended repair and restoration shop.

nelionaudio.com

 

[sae-7125]

a few more photos of the carver m-1.0t amp.


the heat sink seems a bit undersized for so many outputs in close proximity but that does not appear to be a problem for bob's amp design. mk2 series upgrade board as well.


2x4 spacer between amp and preamp to help show thermals, left channel.


right channel, both temps taken after exercising both pairs of bench speakers in parallel (at high volume).


tdk noise filter for mains, nice part number for future reference and projects.

overall a dynamic duo of audio gear with a decent noise floor (silent) and lots of wattage ready for action. should be a fun combination when paired with the large polk sda srs in the demo chamber.

Vintage Polk Audio Speakers: SDA SRS

 

[sae-7125]

testing some elac bookshelf speakers.


elac carina bs243.4

Carina | Bookshelf | BS2434 | Best Audiophile Speakers

Elac - The life of sound | Best Audiophile Speakers

www.elac.com

the speakers have a surprisingly good bass response for such a small driver. it also helps to use an amp with sufficient power reserves and ability, mcintosh ma7900 in the demo chamber seems to do ok.

McIntosh MA7900 Integrated Amplifier

Audio dreams become reality when you play your music through the MA7900 Integrated Amplifier. Combining amp and preamp capabilities, along with a Digital-to-Analog Converter (DAC) and phono section all in one space saving unit, it has the technology and features that music lovers demand.

www.mcintoshlabs.com

 

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Elac Carina BS243.4 loudspeaker Measurements

Sidebar 3: Measurements I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the Elac Carina BS243.4's frequency response in the farfield, and an Earthworks QTC-40 mike for the nearfield responses. The measurements were taken without a grille.

www.stereophile.com

Elac Carina BS243.4 Review (Bookshelf Speaker)

This is a review and detailed measurements of the Elac Carina BS243.4 stand-mount speaker. It is on kind loan from a member and sells for US $999. Even though this is a speaker designed by Andrew Jones, it is a continuation of the line traditionally designed in Germany with much higher sales...

www.audiosciencereview.com

 

[sae-7125]

adjusting the bench speakers.


instead of under the bench now they will be on the shelf, shoulder height.


these were jbl800 but the original woofers had zero foam surround remaining so some salvage drivers were utilized.


8 inch subs (x2) from a monitor audio powered sub that had a major design flaw plus the plate amp expired in a predictable fashion, as they (most brands) usually do.

 

[sae-7125]

back to the conrad johnson pv5 posted a page or three ago.


wrapping up the repair and electrolytic recap.

 

[sae-7125]

the initial problem was stated as sound cutting out.


this system uses an output relay, good place to inspect.


this electrolytic does not look healthy, seems to have wet the bed and now there is a puddle of corrosion.


overall this tube preamp appears to have low hours on it since the board hasnt started to discolor like a previous pv5.

 

[sae-7125]

some pv5 bottles and part numbers.


tung-sol 12ax7 for the phono front end.

Everything you need to know about 12AX7 Tubes - Tubes for Amps

Looking to buy 12AX7 tube but unsure of all the different names and makes? We explain all the things you need to know so you can pick the right one.

www.tubesforamps.com

some tung-sol 5751 for line stage.

Tung-Sol 5751 Preamp Vacuum Tube | www.thetubestore.com

Tung-Sol 5751 preamp vacuum tubes in stock and ready to ship! Find reviews, data sheets and specs to upgrade your tube amplifier.

www.thetubestore.com

5751 - Tube Maze

Reviews of 5751 vacuum tubes and equivalents

tubemaze.info

mains txf with part number c126-128a for future reference.

Standex Acquires Northlake Engineering

STANDEX ACQUIRES NORTHLAKE ENGINEERING Respected Provider of Electromagnetic Products and Solutions Joins Standex Electronic; Positions Standex Electronics to Capitalize on Growth in North American Power Distribution and Medical Equipment Markets; Standex International Corporation (NYSE:SXI)...

standexelectronics.com

PV5 restored and upgraded by Bill Thalmann - Conrad Johnson Owners.com

*wow, i see more than a few issues with this project. probably best that i remain quiet about it.

Conrad-Johnson PV-5 preamplifier

The $1485 PV-5 is a "budget" version of C-J's $2850 Premier Three preamplifier, but according to the manufacturer it embodies much the same kind of circuitry.

www.stereophile.com

*comment #1 has some info.

https://conradjohnson.com/owners-manuals/pv5man.PDF

 

[sae-7125]

measuring some caps on the pv5.


the usual important data when shopping for replacements, 60-90uf 500v


rather large physically not to mention desoldering will be a challenge without damaging/lifting any traces.


the corroded relay circuit cap and its LCR status, not good. looks like a root cause to me.

 

[sae-7125]

original caps removed without issue or pcb damage.


the four tab cathode connections can makes things difficult, good thing this is not a double sided board.


belly pan could use some cleaning. the new 500v caps are sitting on the left side of the photo/bench.


bottom of the board fairly clean and showing low hours of use i.e. no burned pcb areas yet.

in terms of a longevity mod an interesting thought would be to relocate the txf and do a detachable umbilical from main chassis to a outboard power supply box, like the cary SLP-98 posted a few pages ago. either source a larger va txf or do a high efficiency smps which would open up much need air space in the tube heated main chamber.

 

[sae-7125]

finishing up the pv5 repairs.


watching the bottle temps.


mains idle wattage although not at exactly 120v. dim bulb disconnected.


much more space with the new power caps installed. the 1.2k resistor near them hits around 260f during normal operation.

anti-riaa board on the left side for testing the phono section, signal passes through all 8 tubes. sounds slightly better vs the line stage input, lots of gain either way.

 

[sae-7125]

pair of older polk speakers with the time alignment feature.


polk rta 12b speakers with one driver held in place by 1 of its 4 screws, to indicate which driver needs repair. also the tweeter removed from its perch.

Polk Audio RTA 12B Speaker System Review price specs - Hi-Fi Classic

www.hifi-classic.net

First gen Polk RTA 12 recap questions

I have a pair of recently acquired Polk RTA 12's (not 12b, 12c, etc... the first model with the peerless tweets). I want to rebuild the crossovers and need help identifying the caps in use (can't read the values from the physical caps and can't find the schematic for this model on club Polk)...

audiokarma.org

Polk RTA12B info ?

I picked up this set of Polk's and am not finding much information on them . I have looked on the web , Polk forum and here . I think they are eary B's , they have a fuse for the tweeters and MW6600x drivers which the speaker wires are soldered , plus I believe they have the desirable tweeters...

audiokarma.org

installed some dayton drivers to test cabinet for bass response, woofers almost fit (4r+4r wired in series, no rta connection).


cabinets have seen better days and so have the speakers, chunk missing from surround on the right driver. other cabinet in 1st picture a driver has detached voice coil from spider illness.


the tweeter assembly is easy to remove, thumb friendly hardware.


crossover has more than a little going on.


the only place i could find a model model designation, nothing on the cabs just left and right designations.

Polk Audio RTA-12B Vintage Speakers

Buy, sell, and trade thousands of pre-owned audio gear. All tested, certified, and backed by our Certified Pre-Owned Risk-Free Guarantee, with expert HiFi guides to help you at every step.

tmraudio.com

Help! Polk RTA 12.. A,B or C?

Recently picked up an awesome pair of Polk Audio RTA12's I can't tell if they are the RTA12A, RTA12B or RTA12C's can anyone please shed some light on which model these are. They sound amazing and I'm extremely happy with my purchase. Caninets are clean only issue is one of the top grilles is...

audiokarma.org

 

[Bill Ferris]

pair of older polk speakers with the time alignment feature.

View attachment 3297376
polk rta 12b speakers with one driver held in place by 1 of its 4 screws, to indicate which driver needs repair. also the tweeter removed from its perch.

Polk Audio RTA 12B Speaker System Review price specs - Hi-Fi Classic

www.hifi-classic.net

First gen Polk RTA 12 recap questions

I have a pair of recently acquired Polk RTA 12's (not 12b, 12c, etc... the first model with the peerless tweets). I want to rebuild the crossovers and need help identifying the caps in use (can't read the values from the physical caps and can't find the schematic for this model on club Polk)...

audiokarma.org

Polk RTA12B info ?

I picked up this set of Polk's and am not finding much information on them . I have looked on the web , Polk forum and here . I think they are eary B's , they have a fuse for the tweeters and MW6600x drivers which the speaker wires are soldered , plus I believe they have the desirable tweeters...

audiokarma.org

View attachment 3297387
installed some dayton drivers to test cabinet for bass response, woofers almost fit (4r+4r wired in series, no rta connection).

View attachment 3297388
cabinets have seen better days and so have the speakers, chunk missing from surround on the right driver. other cabinet in 1st picture a driver has detached voice coil from spider illness.

View attachment 3297389
the tweeter assembly is easy to remove, thumb friendly hardware.

View attachment 3297390
crossover has more than a little going on.

View attachment 3297391
the only place i could find a model model designation, nothing on the cabs just left and right designations.

Polk Audio RTA-12B Vintage Speakers

Buy, sell, and trade thousands of pre-owned audio gear. All tested, certified, and backed by our Certified Pre-Owned Risk-Free Guarantee, with expert HiFi guides to help you at every step.

tmraudio.com

Help! Polk RTA 12.. A,B or C?

Recently picked up an awesome pair of Polk Audio RTA12's I can't tell if they are the RTA12A, RTA12B or RTA12C's can anyone please shed some light on which model these are. They sound amazing and I'm extremely happy with my purchase. Caninets are clean only issue is one of the top grilles is...

audiokarma.org

And that crossover mounted fuse looks a bit too hardy (too high of amperage rating) like it had been haphazardly replaced sometime back in its abusive user history for a speaker of that size !
I didn`t look at the speakers specifications, just didn`t look right, like it might be a "~ 10 amp" 32 v from the picture !

 

[sae-7125]

And that crossover mounted fuse looks a bit too hardy (too high of amperage rating)

that is a good point, the fuse element seems oversized to protect a tweeter (normally low wattage consumption) or even the time aligned woofer in the cabinet (single wire direct feed).

if the previous owner(s) were blowing fuses on a regular basis it is possible something larger was installed which has a rather predictable outcome. like duct taping a 20a breaker since it keeps kicking, what could possibly go wrong (hello house fire).

 

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RTA 12 Fuse

My son (7yrs) cranked the volume Blew the fuse for the tweeter. It's a 1amp - 250V fuse.

forum.polkaudio.com

looks like i will be examining the fuse in the not so distant future.

RTA 12 info from POLK

Polk sent me some info on Polk RTA 12's. I was having a hard time getting any Brochures on them. Hope this helps someone.

forum.polkaudio.com

https://us.v-cdn.net/5021930/uploads/attachments/7/1/1/9/6/26121.pdf

*brochure info

Polk Audio RTA-12 ‘Real Time Array” Speakers

A pair of the famous first-generation Polk Audio RTA12 “Real Time Array” speakers in excellent condition. Complete with stands. One of the best speakers made in the 1980s: Must be heard.The twin 6.5 inch drivers combine with the 12 inch passive radiator to produce fast but also deep bass. The...

www.canuckaudiomart.com

*note to self: rta = real time array not real time alignment...

 

[Bill Ferris]

that is a good point, the fuse element seems oversized to protect a tweeter (normally low wattage consumption) or even the time aligned woofer in the cabinet (single wire direct feed).

if the previous owner(s) were blowing fuses on a regular basis it is possible something larger was installed which has a rather predictable outcome. like duct taping a 20a breaker since it keeps kicking, what could possibly go wrong (hello house fire).

Probably clipping whatever undersized wattage SS amplification setup the owner was using to achieve higher SPLs than the running out of breath amplifier could cleanly deliver, I`m suspecting, as I`ve seen that effect way too many times over my involvement/exposure in audio reproduction setups !
Duck taped breakers you say, not as bad/dangerous as the older style load centers with the screw in usually glass fuses, that ~50 amp rated copper penny coins could be readily substituted to stop those annoying & tiresome overloaded 15 amp rated circuit fuse blowing events !

 

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~50 amp rated copper penny

i will have to see/measure how many of my coins are in spec, couple of these corroded coins might only handle 40a which would be a disappointment for many of the lake front summer cottages in this area. the ones with cloth covered wiring that predate the carter administration.

although i have heard of one incident involving a .22 cal used as an automotive fuse for headlights. thank you Lewis Black (not for sensitive listeners) for that news briefing, from his y2k white album. his rants on youtube (Lewis Black | 12/8/18 Kansas City MO: Peanut Butter) are enjoyable depending on the viewers preference for entertainment (rip: george carlin and many others).

1998 Urban Legend: Frog Giggin' Accident in Arkansas

1998 Urban Legend: Frog Giggin' Accident in Arkansas: Two local men were seriously injured when their pickup truck left the road and struck a tree near Cotton Patch on state Highway 38 early Monday morning. Woodruff County Deputy Dovey Snyder reported the accident shortly after midnight Monday...

darwinawards.com

 

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doing some research for the pv5 completed earlier. the owner has now expressed interest in the option to upgrade a few things inside, not to mention improve longevity (hello thermal camera critique). so the basic repair and electrolytic recap will be expanded upon to a higher performance level.

http://njsemi.com/datasheets/MDA970A1%20-%20MDA970A6.pdf

the mda970a1 rectifier seems sufficient although running hot even with a heat sink bolted to it (around 85c/185f). the single package rectifier feed the tube heaters so its going to pull some juice.

Tubes 201 - How Vacuum Tubes Really Work

Introduction to Thermionic Valves (Vacuum Tubes)

Introduction to Thermionic Valves (Vacuum Tubes)

colinjs.com

 

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a rather large 200 disc cd changer.


jvc XL-MC222 automatic changer.


some complex mechanical systems under the hood.


no digital output for an external dac.

Mega CD Changers - XL-MC222BK - Features

https://jvc-america.com/cd_players/xl_mc222.html

JVC XL-MC 222 | hifi-wiki.com

hifi-wiki.com

https://ia804504.us.archive.org/23/items/manual_XLMC222_SM_JVC/XLMC222_SM_JVC_text.pdf

*service manual

 

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a few more shots of the 200 disc chassis.


not much in the way of circuit boards but there are a few complex chips here and there.


view of the disc loading mech, vertical positioned module on the right.


multiple board sub-assemblies connected via long ribbon cables. lots of sharp edges from the thin metal frame and support structures.