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


It is currently Dec Sat 04, 2021 2:12 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 4 posts ] 
Author Message
 Post subject: HeathKit UA-1 Voltage Feedback Loop Off 16 Ohm Tap
PostPosted: Sep Wed 22, 2021 8:02 pm 
New Member

Joined: Sep Wed 15, 2021 9:23 pm
Posts: 9
Hello to all. The loop puts 18db back to V1A cathode. The manual says to open the loop for troubleshooting with 1Kh and .09 VRMS at the input and a 16 ohm dummy load. My question is, should I be seeing signal voltage increases at all the signal grids(including EL84’s) if I don’t open the feedback loop? Thanks for any help. Al

_________________
Why is there never enough time to do it right the first time…
But always time to do it over…


Last edited by glowplug53 on Sep Thu 23, 2021 7:28 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: HealthKit UA-1 Voltage Feedback Loop Off 16 Ohm Tap
PostPosted: Sep Wed 22, 2021 8:56 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 18916
Location: Utica, NY 13502 (USA)
Attachment:
File comment: Click on image to enlarge
Heatrhkit UA-1 Schematic.jpg
Heatrhkit UA-1 Schematic.jpg [ 247.42 KiB | Viewed 254 times ]


Dave


Top
 Profile  
 
 Post subject: Re: HeathKit UA-1 Voltage Feedback Loop Off 16 Ohm Tap
PostPosted: Sep Thu 23, 2021 8:28 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5306
Location: Rochester NY USA
The feedback is to the first stage; so its gain is reduced. The remaining stages will have the same levels as when it's running with feedback, though the input level will be much lower. Without feedback, first stage will have a gain of 100 or more, phase inverter has a gain of 1, (and -1 on the second output). So the first stage provides all the gain to the EL84 grids.

_________________
My web page: https://bit.ly/2rxq4qx


Top
 Profile  
 
 Post subject: Re: HeathKit UA-1 Voltage Feedback Loop Off 16 Ohm Tap
PostPosted: Sep Fri 24, 2021 2:32 am 
New Member

Joined: Sep Wed 15, 2021 9:23 pm
Posts: 9
Thanks much Tom. Great explanation. I built these a while back and am just now walking through them with a scope and generator. Al

_________________
Why is there never enough time to do it right the first time…
But always time to do it over…


Top
 Profile  
 
Post New Topic Post Reply  [ 4 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB