I'd like to make a simple 50 amplifier - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th January 2005, 04:02 AM   #1
arnoldc is offline arnoldc  Philippines
diyAudio Member
 
Join Date: Apr 2003
Location: Makati
Send a message via Yahoo to arnoldc
Default I'd like to make a simple 50 amplifier

I was fortunate to be gifted a pair of globe 50s last christmas.

Now I want to make a simple 50 amp using these tubes, and am aware of the 10K grid resistor issue.

What if I use a 417A with plate choke, cap coupled to the 50 with grid choke?

Will the 417A have enough grunt to drive the 50?

If this will work, how do you compute for the driver parameters when using a plate choke?

I'm no designer so pardon my ignorance. But I can use TubeCAD
  Reply With Quote
Old 6th January 2005, 09:55 AM   #2
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: I'd like to make a simple 50 amplifier

Konnichiwa,

Quote:
Originally posted by arnoldc
Now I want to make a simple 50 amp using these tubes, and am aware of the 10K grid resistor issue.

What if I use a 417A with plate choke, cap coupled to the 50 with grid choke?
Sounds fine. I used very much the same scheme when driving a 300B operated rather a lot like a 50 (350V/60mA), main difference was I used a 437A as Driver, at 170V/12mA, not a 417A.

Quote:
Originally posted by arnoldc
Will the 417A have enough grunt to drive the 50?
Yes, you will have to operate the valve quite hard, but it will. Use around 2.5V Bias, 170V Anode or around 220R Cathode resistor and 170V on the Anode. Adjust the +B dropper/decoupling resistor to get the anode voltage right. Under those conditions the 417A should be able to swing around 200V Peak-Peak, enough to drive 300B or 50 well past clipping.

Quote:
Originally posted by arnoldc
If this will work, how do you compute for the driver parameters when using a plate choke?
Same way as for resistor load really, except the Choke approximates a near infinite Anode load but with a low DCR.

If you have a 50 operated at 400V/55mA with -70V Bias (read 1K2 Cathode Resistor) and a 3K5 load you should get 3.5 to 4 watt at clipping and you need a +B of 470V plus Output Transformer losses.

If you take this +B you should use a slow warmup rectifier if you derive the Anode supply for the 417A from that HT line without regulation. If you do, use a pair of "dropper" resistors, giving you RCRC decoupling for the driver stage. This tends to sound better than just RC decoupling.

The kind of anode load chokes I used had around 1K DCR and thus would drop around 12V DC in operation. So, in self bias mode for the 417A we would have a supply to the top of the anode choke of 2.5V (Bias) + 170V (A-K Voltage) +12V or 184.5V. For ease of calculation we use 185V.

If our +B is 475V under normal load we need to drop 290V at 12mA DC current. This suggests 24K for the total resistor in the supply line, using a pair of 12K resistors and 10uF MKP Capacitors should give a nicely filtered 185V for the 417A.

Other options are to derive the Driver +B via Zenner Diodes, Gas Stabilisers, an OB3 and OC2 in series will give around 195V regulated for the 417A driver stage. Or you could use fancy shunt regulators, solid state or hybrid.

You could even build a seperate supply of 185V for the Driver Stage, say rectified with EZ80 and LCLC Filtered. It all depends how far you want to go.

To me a pair of Monoblocks using seperate supplies might be interesting. Of course, if you have seperate supplies you might as well go for direct coupling between driver and power stage and in effect roll the gridhoke and anode load choke into one.

Another note, if you make the heater Supply switchable you could also use 300B's and if you have an Output Transformer with enough primary inductance to allow mistmatching to twice it's nominal 3K5 primary impedance you could select between 300B, 50, VT-52 and VT-25/10Y...

Sayonara
  Reply With Quote
Old 6th January 2005, 10:03 AM   #3
diyAudio Member
 
audiousername's Avatar
 
Join Date: Jul 2004
Location: Melbourne, Victoria
Default Re: I'd like to make a simple 50 amplifier

Quote:
Originally posted by arnoldc
I was fortunate to be gifted a pair of globe 50s last christmas.
You lucky thing! You're making me envious

Quote:
Originally posted by arnoldc
What if I use a 417A with plate choke, cap coupled to the 50 with grid choke?

Will the 417A have enough grunt to drive the 50?
It should work. The 50 has Cgp of around 9pF and a m of around 3.8, so the maximum you'll be looking at for Miller-amplified capacitance is 34.2pF. Add that to Cgf, and strays, you maybe have to charge 60pF or so? I think the 417A would be good enough, but I have no expreience with 50s!

Quote:
Originally posted by arnoldc
If this will work, how do you compute for the driver parameters when using a plate choke?
It's like an output stage, in that the valve faces an inductive load, so it can swing above the B+. And the voltage at the plate is basically B+ (minus the loss by Rdc of the plate choke). The load line is also basically horizontal due to the high impedance presented by the plate and grid chokes - at least at mid-frequency. Things go awry at low frequencies due to the finite amount of inductance, but if you have enough, you don't have to worry about it.

EDIT: Whoops, I see Thorsten posted while I was writing... damn my slow typing
  Reply With Quote
Old 6th January 2005, 10:03 AM   #4
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default POST SCRIPTVM

POST SCRIPTVM

Drop me a line and I zip you up a collection of articles/schematics for the 50 from my files (sorry folks, offer only for Arnold).

Sayonara
  Reply With Quote
Old 8th January 2005, 10:20 AM   #5
diyAudio Member
 
Join Date: Jun 2004
Location: Near Paris
Here is an amplifier I built ( three units ) using three paralleled 6C33 and delivering 50 watts per channel, in Single ended topology.
I attach the upper view and will follow with the view inside.
The power supply is in a separate box and connected with a simple twin wire cable.
The filament and driver transformers are on the main unit (the one shown). THD at full output is 6.5 % - Range 35Hz to 35 kHz
at -3dB .
You can find schematics and full description on AudioXpress magazine, July 2004.
Uses quite expensive OPTs .
Cheers,
Attached Images
File Type: jpg king iii_view.jpg (95.0 KB, 1183 views)
__________________
Ari
  Reply With Quote
Old 8th January 2005, 10:22 AM   #6
diyAudio Member
 
Join Date: Jun 2004
Location: Near Paris
Here is the inside view of the King III.
Bye
Attached Images
File Type: jpg king_inside.jpg (100.0 KB, 1168 views)
__________________
Ari
  Reply With Quote
Old 8th January 2005, 10:24 AM   #7
diyAudio Member
 
Join Date: Jun 2004
Location: Near Paris
Arnold,
I forgot to add that, since the article was published on AudioXpress, some changes have taken place ( not significant but to further simplify this simple amp.
Ari
__________________
Ari
  Reply With Quote
Old 9th January 2005, 04:27 AM   #8
diyAudio Member
 
audiousername's Avatar
 
Join Date: Jul 2004
Location: Melbourne, Victoria


Ari, I think Arnold was wanting to build something with Type 50 triodes, not a 50W amplifier...
  Reply With Quote
Old 9th January 2005, 08:52 AM   #9
diyAudio Member
 
Join Date: Jun 2004
Location: Near Paris
Very sorry,
I must read the threads more carefully.
Thanks for the comment.
Personally I never had the chance of using the 50, but I know it has a wonderful reputation.
By the way, is there a means to classify the valves by reputation ?
Of course this is not necessarily strictly correlated with quality.
Surely those who have a wide experience have some words to say.
It's probably a bad idea. Forget it.
Thanks again.
Ari.
__________________
Ari
  Reply With Quote
Old 9th January 2005, 09:01 AM   #10
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Bonjour Ari,

Your humility is very impressive; I have watched your designs for a long time, Ari, and they are very, very creative, indicating to me at least a fundamental understanding of music........

I was always very impressed with your phase splitter using an EL84 from so long ago - lateral thinking!

And your 6C33C amplifier is impressive; your clever way of using a bipolar power supply is highly unusual. I have a couple, and would like to do something with them. For these low mu tubes do you think there is any advantage in driving the OPT in the cathode circuit rather than the plate? It would surely give a much lower turns ratio, and improve the damping factor?

Cheers,

Hugh
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to make a simple amplifier? mehtadhaval Everything Else 1 16th February 2008 02:23 PM
How would you make this simple PCB or What? KP11520 Chip Amps 11 2nd August 2007 01:47 PM
ok, i'll try and make it simple. PhoenixFL Tubes / Valves 9 13th May 2004 10:04 PM
I want to make a simple UL PP amp arnoldc Tubes / Valves 19 6th March 2004 01:32 AM


New To Site? Need Help?

All times are GMT. The time now is 10:14 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2