Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Sun 17, 2017 2:49 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 10 posts ] 
Author Message
 Post subject: dukane 1a775 amps
PostPosted: Dec Wed 28, 2016 8:10 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 635
Location: Opelika, AL
I have a pair of dukane 1a775 amps that I am going over to use or possibly sell, and was wondering if anyone has any info on them? They are 100W monoblock rack mounted PA amps that use four 8417's as the main drivers, I assume with two parallel sets in push-pull. These don't seem very common compared to other dukane amps that were made, so I've been having a hard time finding out much about them, other than that the 8417 tubes are pretty hard to get, especially at anything resembling a reasonable price.

I've just finally found some info on testing the 8417's in my tube tester thanks to an old thread here.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Tue 03, 2017 1:34 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17981
Location: Warner Robins, GA
You might try asking about the tubes in the tubes and parts section of the forums and see if there are any readily available subs for those tubes.


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Tue 03, 2017 8:56 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 635
Location: Opelika, AL
Unfortunately this is a relatively unique tube that seems to have no equivalent. Low drive needed for relatively high output.

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Tue 03, 2017 10:13 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17981
Location: Warner Robins, GA
Dang.


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Wed 04, 2017 5:56 am 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 282
Location: pensacola fl
The 8417 is a big tube. It can run 600 volts plate and a pair will develop 100 watts. Here is the kicker though it has a very high transconductance of hold on to your seats 23000 which means it takes very little drive on the control grid to to that. 6550 will do 100 watts but needs more drive since its transconductance is 9000 so if you want to sub it you can but rebiasing and getting the additional drive will be needed to start with. Opt will probably work out but is different impedance. The 8417 had problems due to its high performance related to instability meaning parasitic oscillations and even temperature resulting in thermal runaway in some circuits. Look at the line of kt tubes but off hand I can not give a direct sub. If I recall correctly kt150 is the biggest ever made. It can dissipate 70 watts plate and a pair will punch out in the neighborhood of 300 for real watts. The kt 88 or kt 90 or kt 120 may work but i do not have the spec sheets handy. If you sub do your homework as the bias and drive are not all that matters. The heater consumption is also a concern as well as is there room without cramping the tube so it can breathe and not melt down anything near it.
The 8417 and 6550 both have a 35 watt dissipation rating and similar heater requirements but the bias and drive are what to look at there.
Good luck.


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Thu 12, 2017 9:14 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 635
Location: Opelika, AL
So I've got the output transformers measured and have the following info:

primary is center tapped, no ultra linear taps.
there are two secondary windings marked 35V, that have a turns ratio of 15.55:1 (give or take), compared to the primary. These are supposed to be put in series for 70V operation.
there is a center tapped secondary marked 25V that shows a 22.2:1 turns ratio.
there is a feedback winding that has a ratio of 44.4:1

Some questions regarding output transformers:

what happens to primary impedance if I put those two 35V windings in parallel instead of series?
if I use only half of the 25V winding (which would allow primary to essentially have higher impedance to the output stage), am I going to need to de-rate the power handling capability of the transformer?

is the feedback winding possibly usable as an output winding instead? that gives the same nominal impedance to the primary, though it would give an impedance of close to 16K!

I'm looking at other tubes that I could use with these transformers, since a quad of 8417's aren't so easy to find, let alone two sets of them. since I have chassis and output transformers for free, I'm trying to decide what I could do to make a useful set of amps that put out anywhere from 30-100 watts each into 8 ohms (which will more than adequately drive my speakers).

_________________
filling in the gaps in my education...


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Thu 12, 2017 7:26 pm 
Member

Joined: Feb Wed 04, 2015 12:26 am
Posts: 560
the thing about Dukane is they are more than likely PA frequency response (overhead multiple speakers/department store quality sound), and I think you'll be disappointed in the sound quality.

Use the 25v tap for 8 ohm as a test before you go any further.

I hate to be a downer, but you would be better off starting from scratch, dumping the Dukane OT and rebuilding the amp using HI FI o/t.


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Thu 12, 2017 7:47 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 17981
Location: Warner Robins, GA
Depends. They did make some projector related stuff so if this is something related to projection equipment it might have a good frequency response.


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Thu 12, 2017 11:20 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3992
Location: Boston, MA USA
Only DuKane projection equipment I know of is 35mm filmstrip projectors with built-in phonograph for "synchronized" sound. Very lo-fi. No motion picture equipment. Projector amplifiers are like PA amplifiers anyway -- frequency response of a traditional film soundtrack is only 50-7000 Hz.

-David


Top
 Profile  
 
 Post subject: Re: dukane 1a775 amps
PostPosted: Jan Fri 13, 2017 12:11 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 635
Location: Opelika, AL
Artcurus wrote:
the thing about Dukane is they are more than likely PA frequency response (overhead multiple speakers/department store quality sound), and I think you'll be disappointed in the sound quality.

Use the 25v tap for 8 ohm as a test before you go any further.

I hate to be a downer, but you would be better off starting from scratch, dumping the Dukane OT and rebuilding the amp using HI FI o/t.


I had that in mind, but others who had similar bogen amps were able to get decent sound out of them. mostly this is a learning experience, and worst case I sell them to someone to use as guitar amps. My plan was to restore one to original state, and use parts from the other to try something else... compare the sound quality, and decide what to do from there. Keeping all the parts it shouldn't be that hard to put it back together as original.

_________________
filling in the gaps in my education...


Top
 Profile  
 
Post New Topic Post Reply  [ 10 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: Tarpawns and 9 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB