T2p "Plus Zero" push-pull potato amp progress report
- From: jbyrns@xxxxxxx (John Byrns)
- Date: Tue, 07 Mar 2006 13:39:24 -0600
This is a report on the progress of my push-pull potato amp project.
There is only one major design question that remains to be resolved, I
will come to that at the end of this report.
First, I have given the amplifier a name which is the T2p "Plus Zero"
potato amp, in honor of Andre Jute whose work on his 417A T68bis "Minus
Zero" potato amp was the inspiration for my push-pull potato amp design
effort.
Second, with the exception of a few small items of hardware, and the all
important tube, I have all the required parts to construct the amplifier
in my junk box. With the submission of the winning bid for a quartet of
E182CC tubes on eBay yesterday, I hopefully will also have the tube
situation in hand shortly.
To recap the design, the T2p "Plus Zero" potato amp is a push-pull mono
block amplifier using a single E182CC tube. Phase splitting will be done
with a tapped high impedance choke between the two grids with the input
taken directly to one of the grids. I plan to use a line to push-pull
grids input transformer as the choke, with the primary left flapping in
the breeze as it were. This input/phase splitting scheme is a compromise
to fit the parts I have available in my junk box. My original plan was to
use an input transformer with a high impedance primary winding, and a
turns ratio of 1:3 from the primary to the total secondary, but these
transformers are hard to find on the second hand market and expensive when
they are found. So I will use the choke approach until I can find a
suitable transformer, which leaves me about 3 dB short of the desired
input sensitivity.
The output transformer is a Hammond unit with a 10k center tapped primary
and 4-8-16 Ohm secondary taps.
The power transformer will be a Stancor unit that has a 6.3 volt heater
winding and a 125 volt 50 mA B+ winding. With a full wave bridge
semiconductor rectifier this should provide the required 162 volts of B+
plate to cathode at 40 mA, even with some allowance for the use of cathode
bias, although it isn't clear how much voltage drop will be available for
a pi filter.
I would prefer doing a stereo amplifier in the first go around, but I only
have one output transformer, and the power transformer isn't large enough
for a stereo amplifier, so I guess I will have to consider this a
breadboard and if I like it do a stereo version, or try to find matching
parts to do a second mono block.
The question that remains to be resolved is what sort of bias scheme to
use? The three choices are cathode or self bias, fixed bias provided by a
rectifier off the heater supply, or back bias which is a variant of
cathode bias which has the advantage of eliminating the impedance in the
cathode circuit which is common to the grid and plate circuits. If
cathode bias is to be used, there are a couple of secondary questions,
should a single cathode resistor be used, or should each tube have its own
cathode resistor? And if a single cathode resistor is used should it be
bypassed with a capacitor?
I would welcome any thoughts or opinions on what bias scheme would be best.
Regards,
John Byrns
Surf my web pages at, http://users.rcn.com/jbyrns/
.
- Follow-Ups:
- Re: T2p "Plus Zero" push-pull potato amp progress report
- From: Andre Jute
- Re: T2p "Plus Zero" push-pull potato amp progress report
- Prev by Date: Re: On the triode model at work in the T68bis "Minus Zero" potato amp
- Next by Date: Re: Hybrid Circuit
- Previous by thread: Re: Hybrid Circuit
- Next by thread: Re: T2p "Plus Zero" push-pull potato amp progress report
- Index(es):
Relevant Pages
|
