Reply to topic  [ 7 posts ] 
Bugera 1960 power amp conversion 
Author Message
Hall of Fame Member
User avatar

Joined: Sun Jan 20, 2013 9:22 am
Posts: 3104
Location: Manchestoh, UK
As a quick aside from my rack preamp goofings off I'm converting a busted bugera 1960 a friend game me years ago into a dedicated power amp.
The OT is shot and quite convincingly failed the neon short test so it's a paper weight at best unless I ever fancy a go at rewinding it, which I don't. Thankfully I have a spare 100W 4K primary OT in my spare parts pile and the PT is good for somewhere between 480-500VDC which is premium KT88 territory for a single rail.

Design wise I'm plumping for a parallel input buffer and long tailed pair PI. It'll have a very SLO looking set of power amp controls. I may swap the presence for a 5k scratchy type and the depth for a CCV type. There is also a pot to set the amount of NFB which will control the power amp feel from tight to loose. I may also put a pot in line with the 470r LTPI bias resistor as an additional sort of MV which will allow the PI to break up at a lower volumes but this might be better suited to a switch.

Image

The power supply will be slightly unconventional as I want to try out a regulated screen supply, rather than use the original choke feed. This has the advantage that running the screens at a rock solid 400VDC will put way less stress on the screens while still delivering full power and punch. I can also feed the LTPI straight off this node too as well as implement current limiting if there is a screen short. You'd only really notice the difference between this and the choke at super high volumes and I want a big solid bottom end which is better achieved with regulation.

Image

Here is a quick test of the PT to check it's doing what I expect. 508VDC unloaded. More on this tonight.

Image


Thu Sep 27, 2018 1:28 am
Profile
Hall of Fame Member
User avatar

Joined: Tue Feb 12, 2013 10:59 pm
Posts: 4413
Location: So Cal
Cool... :thu: Did you finish it? If so, howd it go?


Sat Oct 06, 2018 6:14 pm
Profile
Hall of Fame Member
User avatar

Joined: Sun Jan 20, 2013 9:22 am
Posts: 3104
Location: Manchestoh, UK
I went on vacation : lol:
It's the first thing in doing when I get back though.


Sat Oct 06, 2018 9:46 pm
Profile
Hall of Fame Member
User avatar

Joined: Sun Jan 20, 2013 9:22 am
Posts: 3104
Location: Manchestoh, UK
Back from vacation, time to get on this. I have too many ideas to work on that need a dedicated power amp to test...


Wed Oct 17, 2018 9:31 am
Profile
Hall of Fame Member
User avatar

Joined: Mon Jan 21, 2013 12:35 pm
Posts: 738
Zozobra wrote:
As a quick aside from my rack preamp goofings off I'm converting a busted bugera 1960 a friend game me years ago into a dedicated power amp.
The OT is shot and quite convincingly failed the neon short test so it's a paper weight at best unless I ever fancy a go at rewinding it, which I don't. Thankfully I have a spare 100W 4K primary OT in my spare parts pile and the PT is good for somewhere between 480-500VDC which is premium KT88 territory for a single rail.

Design wise I'm plumping for a parallel input buffer and long tailed pair PI. It'll have a very SLO looking set of power amp controls. I may swap the presence for a 5k scratchy type and the depth for a CCV type. There is also a pot to set the amount of NFB which will control the power amp feel from tight to loose. I may also put a pot in line with the 470r LTPI bias resistor as an additional sort of MV which will allow the PI to break up at a lower volumes but this might be better suited to a switch.

Image

The power supply will be slightly unconventional as I want to try out a regulated screen supply, rather than use the original choke feed. This has the advantage that running the screens at a rock solid 400VDC will put way less stress on the screens while still delivering full power and punch. I can also feed the LTPI straight off this node too as well as implement current limiting if there is a screen short. You'd only really notice the difference between this and the choke at super high volumes and I want a big solid bottom end which is better achieved with regulation.

Image

Here is a quick test of the PT to check it's doing what I expect. 508VDC unloaded. More on this tonight.

Image



Congratulations on intimidating the shit out of me!! :lol:

_________________
After Tuesday, even the calendar goes WTF!


Wed Oct 17, 2018 10:05 am
Profile
GABmiral
User avatar

Joined: Sat Jul 20, 2013 9:35 pm
Posts: 15295
Location: Same town as Lindsay Lohan, Amy Fisher, Joey Buttafucco & Debbie Gibson
Looking forward to watching the conversion - your build threads are awesome! :rawk:

_________________
1969 Sunn Solarus ● 2x 1980's Randall RG-80 ● 2013 Hi-Tone HT103-DG (Winner Best Rig 2014) ● 2015 Mortatone 12/15 Cab w/EV SRO's ● 2017 Jubilee ● Incoming Ceriatone Model Tee
Walt wrote:
But when the hour is nigh, and the lights are low, and I got a little toothpick of a shwag joint in my teeth, and my friends want to hear me play "Into the Void", or "TNT", "or "Cemetery Gates"...I plug my 600 dollar guitar into my 150 dollar amp, and I am a Rawk gawd.


Wed Oct 17, 2018 10:12 am
Profile
Hall of Fame Member
User avatar

Joined: Sun Jan 20, 2013 9:22 am
Posts: 3104
Location: Manchestoh, UK
Planning the bias supply and regulated screen supply layout. I just going to use the half wave bias supply that was in the Bugera and pretty much every other Marshall clone with it's own bias winding on the Px but I've decided why half arse it and will go with a full bridge.

I have somehow lost the 200V Zener diodes for the regulator though :( Yet another order to RS it is...


Wed Oct 17, 2018 11:45 am
Profile
Display posts from previous:  Sort by  
Reply to topic   [ 7 posts ] 

Who is online

Users browsing this forum: No registered users and 13 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  




Powered by phpBB® Forum Software © phpBB Group