Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Sat 27, 2021 7:19 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 11 posts ] 
Author Message
 Post subject: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Thu 09, 2021 3:26 am 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 815
Hi,

I'm currently in the process of restoring a very old PRESTO 85B (disc cutting) amplifier. It's a big rackmount unit, basically a simple transformer coupled push pull amp using (2) 6L6G's and (4) 6SJ7's. The problem is that the unit in my possession has been heavily modified and I would like to put it back to its original condition, or at least as close as possible. Unfortunately the only (hand drawn) schematic available on the web is incorrect and I was unable to find any more informations about this amp so far.

Thus, if you have the (original) PRESTO 85B schematics and/or manual in your files I would greatly appreciate If you could post a scan, or alternatively a web (link) source where I could buy a copy of the 85B manual.

Thanks to all for your help.


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Thu 09, 2021 5:13 am 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 7594
This place claims to have 85A &E information (I think the difference for the B was being rack mounted), for $15.

http://www.prestohistory.com/Presto4.html

I know nothing about them.

Is this the site with the hand drawn schematic you believe to be wrong? https://www.omroepmuseum.be/index.php/4 ... presto-85b

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Last edited by Eickerman on Sep Thu 09, 2021 5:26 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Thu 09, 2021 5:25 am 
Member
User avatar

Joined: Jan Fri 06, 2012 8:47 pm
Posts: 7594
After doing a Google Translate on the website with the hand drawn schematic I found that they said, "It was also revealed that a lot of changes had been made to both devices, making it practically impossible to bring them back to their original state. (After all, as far as we know, there is no original diagram or document available about this). "

So, not sure about the other site that says they have a schematic.

Curtis Eickerman

_________________
http://curtiseickerman.weebly.com


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Thu 09, 2021 1:01 pm 
Member
User avatar

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 11281
Location: Sunbury, Ohio 43074
Great project, and I hope you are successful. I was just reading an old electronics magazine that mentioned their next issue would go into the details of the Presto, but the article did not say specifically what model. I'll see if I can dig up the "next" issue, but it probably won't be till after Kutztown.

best...

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Thu 09, 2021 5:08 pm 
Member

Joined: May Wed 16, 2012 6:58 pm
Posts: 317
Location: Eastlake, Michigan
Have a PDF manual for the Presto 90-B recording amplifier if you'd like it


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Fri 10, 2021 6:39 pm 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 815
Eickerman wrote:
After doing a Google Translate on the website with the hand drawn schematic I found that they said, "It was also revealed that a lot of changes had been made to both devices, making it practically impossible to bring them back to their original state. (After all, as far as we know, there is no original diagram or document available about this). "

So, not sure about the other site that says they have a schematic.

Curtis Eickerman


Thank you for your help. I already went to this website and since I understand dutch (flemish) I had no translation issues. My 85-B is very likely from the same origin and cosmetically in poor shape (mostly dust and grime) but with all transformers tested good. Electrical restoration is allmost complete but there are still some unknows regarding some parts values and circuits changes which are different from the (hand drawn) schematic posted.

I'll keep searching and will post pictures of the restored amp when finished.


Last edited by Tubologic on Sep Sat 11, 2021 4:34 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Fri 10, 2021 6:49 pm 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 815
mr_ed01 wrote:
Have a PDF manual for the Presto 90-B recording amplifier if you'd like it


Thank you for your kind offer, but I think the 90-B has a completely different circuit inside.


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Sep Fri 10, 2021 6:54 pm 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 815
Barry H Bennett wrote:
Great project, and I hope you are successful. I was just reading an old electronics magazine that mentioned their next issue would go into the details of the Presto, but the article did not say specifically what model. I'll see if I can dig up the "next" issue, but it probably won't be till after Kutztown.

best...


That would be nice... maybe there was an article in an old issue of Audio or other (Hi-Fi, broadcast,...) magazines. I can't date this amp but I would guess something like mid 40ies - early 50ies, this should help narrowing your search.


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Oct Wed 06, 2021 12:09 am 
Member
User avatar

Joined: Apr Sat 04, 2015 6:15 am
Posts: 1988
Location: Dos Rios, CA. region
You might try looking at David Bogen for sources of the 85B schematic,
not sure if the companies had merged by the time of your amp's manufacture or not.
I've come across the presto cutting amps in old radio and audio mags as well, but there's a lot to go through to check.
The American radio history (or world radio history?) site may have catalogs and copies of those mags,
if we knew the year/date of product release or manufacture of the 85B that would be helpful in finding an article (w/schematic) on that model.

_________________
"How come we never watch Television?" - sonuva TV repairman in the fifties, Mac Rebennack.


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Oct Wed 06, 2021 12:30 am 
Member
User avatar

Joined: Jul Mon 08, 2013 2:48 pm
Posts: 815
ampstamp88 wrote:
You might try looking at David Bogen for sources of the 85B schematic,
not sure if the companies had merged by the time of your amp's manufacture or not.
I've come across the presto cutting amps in old radio and audio mags as well, but there's a lot to go through to check.
The American radio history (or world radio history?) site may have catalogs and copies of those mags,
if we knew the year/date of product release or manufacture of the 85B that would be helpful in finding an article (w/schematic) on that model.


Thank you for your help and suggestions. I think the Bogen-Presto merging came much later, well after this amp was manufactured. (I would roughly date it circa 1947- 1955) My exemplar is S/N 2404, if that could help. I checked all my old issues of AUDIO and FM/TV magazines of that period but found nothing (but a few small adverts) about the 85B. Since this amp was a part of a disc cutting system maybe something could be found in a specialized magazine about (disc) recording but I have no idea if there ever was such a magazine.
I found a few Presto schematics in Oliver Read's The Recording and Reproduction of Sound but unfortunately nothing about the 85B. Maybe another book about recording/disc cutting has more infos ?


Top
 Profile  
 
 Post subject: Re: PRESTO 85-B (cutting) amplifier infos needed
PostPosted: Oct Thu 07, 2021 2:30 am 
Member
User avatar

Joined: Apr Sat 04, 2015 6:15 am
Posts: 1988
Location: Dos Rios, CA. region
I looked through a bit of my catalog collection and came across this ad clipped from a 1949 Newark catalog,
showing the 87A amplifier. I would hazard to guess the 85B is a year or 2 older in date of manufacture, does the "2-piece" unit shown here look at all
like the 85B in cosmetic appearance?
Attachment:
Presto 87A 1949 Newark.jpg
Presto 87A 1949 Newark.jpg [ 503.45 KiB | Viewed 327 times ]

_________________
"How come we never watch Television?" - sonuva TV repairman in the fifties, Mac Rebennack.


Top
 Profile  
 
Post New Topic Post Reply  [ 11 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 6 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB