Search found 10544 matches

by Cressy Snr
Sat Dec 04, 2010 9:28 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

So here it is:

Image

The two HT dropper resistors for the first and second stages will have to be
adjusted on test.

It looks OK to me but I may have missed something.

Steve
by Cressy Snr
Sat Dec 04, 2010 12:32 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

this may be my usual 'foot in mouth' question...but... how does v3 cathode see ground...I can't fathom how there is a circuit there..... It's OK Ed The diagram is only a very very rough schematic (hurriedly put together) to give me an idea of what I'm going to do. You're right of course about there...
by Cressy Snr
Sat Dec 04, 2010 10:01 am
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

Cheers Phil

I'll be in touch with Phil@Bluebell after Christmas for some of the bits, so I'll add those to my list.

Steve
by Cressy Snr
Sat Dec 04, 2010 9:40 am
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

pre65 wrote:I see you have a 63mh choke in the filament supply.

Is that one of those e-bay ones ?
Yep

I got half a dozen of them on Will's recommendation a couple of years ago.
by Cressy Snr
Sat Dec 04, 2010 7:31 am
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

Cheers Nick,

Swotting up on A2, I must have read several times that caps and A2 don't mix, yet still I bung in a cap precisely where it's not wanted :roll:
by Cressy Snr
Sat Dec 04, 2010 12:33 am
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

Here's a preliminary schematic for zero biasing of the output valve. The main power supply is included plus the 10V DC filament supply for the 8005. http://web.me.com/scress1958/Pictures/8005schem.gif Any thoughts? Instinct tells me that the cap is needed at the bottom of the IT secondary to isolate...
by Cressy Snr
Thu Dec 02, 2010 6:27 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

Yep

16wpc single ended from transmitter valve just cruising along ain't something to be sniffed at. :)

Just hope I can design something to do the valve justice.

I've never done A2 zero bias before so it's a whole new ball game.

So stand by to point and laugh at my schematics :lol:

Steve
by Cressy Snr
Thu Dec 02, 2010 5:33 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

What do you get out of the 13E1 amp Steve? I get around 11WPC out of the 13E1. 16WPC single-ended is just possible with a 13E1 but you're running at around 85 watts plate dissipation and near enough 200mA current with 450V on the plates. OTOH, 11WPC sounds bloody good out of a 13E1, so the OT100 va...
by Cressy Snr
Thu Dec 02, 2010 5:24 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

Right! So a tiny compromise. With a 5K OPT, 600V @ 100mA fell very conveniently on the zero bias line so that's what I chose, giving a plate diss of 60W. http://web.me.com/scress1958/Pictures/OT100600V.gif Almost double the previous power output at 16WPC (that's more like it) nice and linear etc. I ...
by Cressy Snr
Thu Dec 02, 2010 4:22 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

Mike H wrote:70W? Should be



Cheers Mike,

I'll re-examine the HT and operating conditions for the valve.

Steve
by Cressy Snr
Wed Dec 01, 2010 9:29 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

Hi Nick, Funnily enough, 700V @ 100mA was what I was originally considering, but chickened out when I read the data sheet. I got frightened off by the class B designation for the max dissipation of 75W The 700V operating point would certainly be better in terms of power output. Do you reckon the dis...
by Cressy Snr
Wed Dec 01, 2010 8:34 pm
Forum: Everyones Projects
Topic: OT100/8005 Amplifier
Replies: 45
Views: 17485

OT100/8005 Amplifier

Ideas for an op point would be welcome. Transformer drive with zero bias might be nice looking at the curves. Maybe 450V, 50mA, 0 bias? Or, 450V, 100mA, +10V bias. Looks like needs about 10mA for the grid if it goes to +20V So I took this from the "valves" thread and have decided that it ...
by Cressy Snr
Tue Nov 30, 2010 8:13 pm
Forum: Valves
Topic: OT100/8005
Replies: 3
Views: 3169

OT100/8005

Managed to pick up a pair of these babies for £58 off ebay. They were used in the Macintosh M1 series of amplifiers in the '50s. http://web.me.com/scress1958/Pictures/8005.jpg This particular pair were made in the 70s by Tungsram. Here are the curves: http://frank.pocnet.net/sheets/049/8/8005.pdf I ...
by Cressy Snr
Sun Nov 28, 2010 8:05 am
Forum: Your Fave Artists
Topic: One for all you groovy hep cats
Replies: 16
Views: 4377

Mose's da man 8)

Here's a classic mod toon from Junior Wells



The intro sounds like a valve amp enthusiast trying to remove a hot tube with bare hands. We've all been there :D
by Cressy Snr
Sat Nov 27, 2010 9:29 pm
Forum: Your Fave Artists
Topic: One for all you groovy hep cats
Replies: 16
Views: 4377

OK Man

Here's uncle Billy from '72