Jackson 561 Tube Tester

This article will discuss repair and calibration of the Jackson 561 tube tester. High voltages are present, repairs should only be attempted by a qualified technician. Copyrighted, all rights reserved.


The Jackson 561 appears to be a rare (uncommon) model. Very little documentation exists, and I have seen only a small number of them for sale.

The model 561 is a combination of the Jackson 634 and the 648. Photo below shows Jackson 561 (right); Jackson 648A (left).

Comparison: Jackson 648A vs 561


If the 634 and 648 mated, the 561 would be its offspring. It shares the following characteristics from the 648: (a) the same meter, (b) variable leakage control, (c) color scheme, and (d) case design. From the 634, it shares (a) the same test method (which Jackson calls “Dynamic Output”), (b) Shorts Test control, (c) lack of a Noise test, and (d) function control layout. In fact, the 634 tube setup chart can be used (with slight modification) with the 561, as explained later.


Jackson 634 Tube Tester

If you appreciate vintage tube test gear, you will enjoy this 1940 vintage Jackson 634 Tube Tester. It is an excellent choice for anyone looking for a quality, well-built, tester that can test the VERY OLD tubes, such as #50, 01A, 1V, #10, 2A3, #15, #19, HY113, HY115, HY125, #26, #45, 71-A, #83, etc.

This article is also relevant to Jackson 637 tester, which is same as model 634 tester with additional integrated multimeter functionality (volts and ohms testing).

(Jackson 634 testing Cunningham CX-350 Globe #50 Triode tube)

Jackson 634 testing Cunningham CX-350 Globe #50 Triode tube

What is really “cool” about this tester is its very small size. Measuring only 8.5 x 8.5 x 6 inches and weighing 9 lbs, this unit packs a big punch in a small size!

This tester has been in my personal collection since 1990, and it is the oldest tester in my collection (except for a Supreme 550 Radio Tester from 1936, which also has some basic tube testing capability).

Jackson 634 - 637 modernization bulletin

Jackson 634 – 637 modernization bulletin. Click to enlarge.

This tester is so old that it did NOT come with a 9-pin-miniature socket installed — that was too modern!

(Article UPDATE, Nov 3, 2008): I found an original Jackson modernization bulletin, and the Jackson 634 and 637 testers were released in 1939. All 1939 models were sold without the 9-pin-miniature socket installed. The 1940 models were already modernized at the factory.

I have installed a new 9-pin-miniature socket, and will teach you how to “modernize” your 1939 vintage Jackson 634 also. (Jackson sockets are wired unique, and do not correspond to the 1-to-1, 2-to-2, wiring that many testers employ).

Service information and many additional photos are as follows…


Hickok 6000 socket saver installation

This article will discuss my method of professionally installing a socket saver into the socket panel of a Hickok 6000 / 6000A / 6005 tube tester, and is designed so that (1) you cannot even see that a socket saver is installed, (2) the case lid will close normally, and (3) the socket saver is easily replaceable when it wears out.

The Hickok 6000-series of tube testers use a plug-in socket panel instead of individual sockets affixed to the chassis. The socket panel protrudes upward, and there is no extra room between the socket panel and the case lid. Therefore, traditional installation of a socket saver (plugging it into an existing socket) is unacceptable for these testers because the case lid will not close.

Fortunately, if you are willing put forth effort, you can have your cake and eat it too! This project will demonstrate a 9-pin miniature socket saver installation, but the process can be adapted for other sockets.

When you are finished, here is what you will accomplish:

Hickok 6000 after professional installation of socket saver

Photo above shows Hickok 6000 after my method of professionally installing the socket saver. It is impossible to see that a socket saver is even installed!


B&K 700 & 707 tube tester

©2008, Bob Putnak.  All rights reserved.  This article discusses the B&K 707 Dyna-Jet Dynamic Mutual Conductance tube tester, including repair and calibration. The discussion is also relevant to the B&K 700 (the 700 is almost identical except for socket configuration) and some of the information is applicable to the B&K 650.

To jump immediately to the section that explains the Upgrades and Mods that I find useful, click HERE.

BK 700

BK 700

my BK 707 with custom TubeSound plate current meter upgrade

The B&K 707 tube tester dates from the late 1960s into the 1970s. My manual is stamped August 1969, and a modern tube data setup chart dates 1978.

First of all, a brief explanation of the circuitry of this tester is necessary. Is this a Mutual Conductance tube tester? Well, yes and no.

Tubes that test in the “Jet-Check” section test for mutual conductance, with the exception of diodes/rectifiers (which always test only for Emission). The Jet-Check section is the upper panel (sockets 1 – 35). Tubes that test in the “Switch” section — the bottom panel (sockets 36 – 45), are tested for Emission.


Marathon MX-280 Globe tube MESH PLATE

Here is a rare tube — a Marathon MX-280 Globe #80 rectifier tube featuring MESH PLATES construction!  Not only that, but each section tests very strong Emission, comparable to an NOS #80!

Mesh Plate Marathon MX-280 Globe rectifier tube

In 18 years of collecting, I do not remember ever seeing another Mesh Plates #80 tube.  Look at that Glow!  You can see right through the Mesh Plates into the filament!


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