ARRL

Forum Home - Rules - Help - Login - Forgot Password
Members can access, post and reply to the forums below. Before you do, please first read the RULES.

The "JUNKER" AMP

Oct 28th 2011, 12:08

N8CHR

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I ran across an articile for an amp. It's called the "Junker" amp in the 1966 QST. It can be build using a pair of 811's. I have most of the parts I need. Has anyone ever build this amp? Does anyone have another fairly easy amp circuit and construction articles using these tubes and old tv transformers? No money, but I can nickle dime for the parts. XYL is ok with that. "if you know what I mean". There is also a Ham Fest in Massillon, Ohio this Sunday so I'll be there. Thanks TOM N8CHR
Oct 28th 2011, 19:45

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0


Here is the original 1966 article by Lew W1ICP

• Feb 1966 - QST (Pg. 15)
Low-Cost 700-Watt Linear Amplifier, A
Author: McCoy, Lew, W1ICP

http://p1k.arrl.org/pubs_archive/54913

Grounded grid using a pair of 572Bs for 700 watts input. (which is different from the current output standard) In most modern stations, it would be wise to install a tuned input circuit.

A common mistakes with grounded grid amplifiers is to forget that the input and output are in series, and interact with each other. You can go nuts trying to fix the output tuning if you think that you can compensate for a poor input circuit by just running more power into the amplifier--they have to work together. The Bill Orr Radio Handbook has a good description on how the input circuit not only acts as a flywheel to smooth out the input impedance of the amplifier, but decouples the cathode current spikes from the rest of the station.

Zack Lau W1VT


ARRL Senior Lab Engineer
Nov 1st 2011, 07:14

KE8DO

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I have not read the QST article but I will comment anyway. I remember the big heavy transformers that the big old black and white TV's had from back in the 1960s. My dad worked for a Philco TV dealer and he would bring home junk TVs for me that they had taken in on trade. They had a center tapped winding for a full wave tube type rectifier for a B+ of about 350V or maybe more, if my memory is correct. You could use the same winding to get about 1500 V or more using a voltage doubler circuit and solid state rectifiers. I never did build a homebrew amplifier, but I did built a SB-220 from a kit, and I did use a used TV transformer to build a power supply for my HW-100 and HW-32. It may be very hard to find one of the old tube type TVs today. Be careful working with the HV.
Let us know how it turns out.
73 and good luck - Don KE8DO

Back to Top