EL509 OTL Amplifier
-
- Amstrad Tower of Power
- Posts: 10552
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#16
Changed my mind now.
This looks better and I reckon the 12ax7 is still far enough from the mains transformer.
6C33s like those Joule Electras?
"Throw the switch Ygor"
"Yes Master"
This looks better and I reckon the 12ax7 is still far enough from the mains transformer.
6C33s like those Joule Electras?
"Throw the switch Ygor"
"Yes Master"
#17
I should be able to start playing with the 6c33c's soon. Hopefully I will just have heat from the valves, as I am using fixed bias, so no cathode resistor. The 7A of heater current per valve will be fun though.
Thats a mighty big TX you have there steve for the bias supply. What current are you expecting to provide?
Thats a mighty big TX you have there steve for the bias supply. What current are you expecting to provide?
-
- Amstrad Tower of Power
- Posts: 10552
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#18
Exactly Nick.Nick wrote: Thats a mighty big TX you have there steve for the bias supply. What current are you expecting to provide?
It was the only one I could find in my box with the right output voltage and cheapskate that I am I thought I might as well make use of it. It is a bit big but it'll do for now.
Here is the layout with a 12B4A preamp stage built in.
Anyone for 15 pin bowling?
The board is 2 feet by 18in so building it as an integrated will be a suitable solution to the size problem. When my missus saw the size of the thing she said something I can't repeat for young ears
Steve
#19
I know the feeling. I am hoping that the custom torroid I am waiting for is ok, as I guess that sort of thing would be good for the sort of amp you are building, and in theory, it could go inside the box, given that you have no OP TX's to worry about.and cheapskate that I am I thought I might as well make use of it.
-
- Amstrad Tower of Power
- Posts: 10552
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#20
Well I've gotten started on the OTL.
I've decided to take a modular approach to the build. This means that each bit can be built and tested before putting it into the finished circuit. I don't want any spectacular stuff when I fire it up.
The first module underway is the power stage. This comprises eight EL509s; four per channel.
The positve HT is fed by the red cables and the negative HT fed with the black cables. The heater wiring loom will be fed in on the opposite side of the output board. The bus bar running up the centre of each tube bank is the output rail which in the finished amp will be connected direct to the positive terminal of each speaker output pair.
Steve
I've decided to take a modular approach to the build. This means that each bit can be built and tested before putting it into the finished circuit. I don't want any spectacular stuff when I fire it up.
The first module underway is the power stage. This comprises eight EL509s; four per channel.
The positve HT is fed by the red cables and the negative HT fed with the black cables. The heater wiring loom will be fed in on the opposite side of the output board. The bus bar running up the centre of each tube bank is the output rail which in the finished amp will be connected direct to the positive terminal of each speaker output pair.
Steve
-
- Amstrad Tower of Power
- Posts: 10552
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#21
The output stage module is completed
Input/driver stage is next on the list.
Steve
Input/driver stage is next on the list.
Steve
- Dave the bass
- Amstrad Tower of Power
- Posts: 12273
- Joined: Tue May 22, 2007 4:36 pm
- Location: NW Kent, Darn Sarf innit.
-
- Amstrad Tower of Power
- Posts: 10552
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#23
So now we have heaters!
The driver stage heaters have been wired up and the whole thing tested with raw AC from the 20V heater transformer.
The rig has been on soak test for the past three hours with no mishaps.
Voltages are stable and read correctly with just the unrectified output from the heater TX.
Heater transformer gets very warm but that is only to be expected with that lot to power.
Well something works anyway.
Steve
The driver stage heaters have been wired up and the whole thing tested with raw AC from the 20V heater transformer.
The rig has been on soak test for the past three hours with no mishaps.
Voltages are stable and read correctly with just the unrectified output from the heater TX.
Heater transformer gets very warm but that is only to be expected with that lot to power.
Well something works anyway.
Steve
-
- Amstrad Tower of Power
- Posts: 10552
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#27
Aww come on lads; you know me better than that.
The aluminium plates are actually subchassis sections which facilitate the modular construction technique.
They will be stood off the underside of a varnished birch top plate and the valves will poke up through the wooden surface with sufficient space around the bases to avoid discolouration.
Steve
The aluminium plates are actually subchassis sections which facilitate the modular construction technique.
They will be stood off the underside of a varnished birch top plate and the valves will poke up through the wooden surface with sufficient space around the bases to avoid discolouration.
Steve
- Dave the bass
- Amstrad Tower of Power
- Posts: 12273
- Joined: Tue May 22, 2007 4:36 pm
- Location: NW Kent, Darn Sarf innit.
#29
Thats just slack Aincha never heard of 2nd hand MDF and plySteveTheShadow wrote:
They will be stood off the underside of a varnished birch top plate and the valves will poke up through the wooden surface with sufficient space around the bases to avoid discolouration.
Steve
DTB
"The fat bourgeois and his doppelganger"
-
- Amstrad Tower of Power
- Posts: 10552
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#30
Here is the driver stage about a third of the way done.
This needed some serious thinking about what to put where, particularly as I decided to stick a 12B4a preamp stage in there as well.
I've got it all to do again at the other end of the board now
How Andrew shoehorned a similar thing plus a PSU into that little copper box I'd love to know.
Come back Loftin & White - all is forgiven
Steve
This needed some serious thinking about what to put where, particularly as I decided to stick a 12B4a preamp stage in there as well.
I've got it all to do again at the other end of the board now
How Andrew shoehorned a similar thing plus a PSU into that little copper box I'd love to know.
Come back Loftin & White - all is forgiven
Steve