The first $64,000 dollar question for all hand wired test equipment, factory wire or Kit is it wired right.
I have found four factory wire EICO 667 that were wired wrong from the factory and a large number of kits. EICO are not the only ones. Hickok two 6000, one 539, two 799 all missed wired from factory. Then there are the Cardmatic Military models: AN/USM-118A and later TV-7-D’s both missed wired and sections not solder.
There are stories that the government canceled the contracts and the company’s shipped everything.

I have an errata sheet for the EICO 667 Assembly Instructions some place. I look for it this weekend.

Jimmie

Hey Jimmie,

I was just "under the hood" of my EICO 667 last weekend. Put in several replacement caps and resistors..... calibrated and added some meter movement protection....

It's a veritable rat's nest in there...... all those ganged lever switches. I can see how mistakes could be made......

I looked at a couple of common dual triodes like 12AU7, 6SN7 Etc. on the roll chart of my Hickok KS-15750-L1 tube tester and for dual triodes the settings for both sides is the same. the switches have to be changed to select which section you test but things like Bias are identical.

For Dual Diodes like 80, 5U4, Etc which are direct heated, there is a slightly different setting for each side. For heater Cathode dual diodes like 6X4, again the same settings.

I had concluded this related to internal filament connections in the tube tester.

I most recently noticed this while trying to find a good "S" style 80.
I thought it was an error on the roll-chart but I checked some other types and they were similar. When you set to the roll-chart you usually get the same reading side to side.

I would expect the tubes themselves are reasonably identical side to side when new. Depending on use over time I would expect some imbalance would creep in.

There are some dual triodes made for Flip-Flop use that were supposed to remain balanced even when one triode was left turned on for a long time.

Jim

I can understand where filament tubes might have slightly different settings for each side. It would depend on which filament lead was used for negative (ground). One side would be offset by filament voltage.

You hit it right on the nail head,Alan.Those charts are supposed to guide you in making up your own settings for tubes.You are supposed to consult a tube manual,find out what the maximum plate current for the tube is supposed to be,find out what maximumum plate voltage is,and consult those charts to set the controls accordingly.This is where things get strange.Eico seemed to ignore these rules,or directions, when it came to their test data for many tubes.

When you monitor the plate current of a 12AX7,which is supposed to have a maximum plate current of around 3 ma and the Fluke 179 is reading 15 ,somebody didn't pay much attention to what they were doing.I guess this is where the afore-mentioned "knob twiddling" must have come in.Of course,they issued all kinds of addendums to fix these mistakes,but some of this data was just as screwed up,and some they eventually got right.

I guess what I've been saying is,to get along with one of these units,you have to be willing to do some experimenting to see which settings work,and which don't.

In addition to the (electrical) arguments posted above, I somtimes prefer to use the single-line test setups (on testers including Eico 666, 667, Simpson 1000, Heathkit TT1, etc) because they require fewer switch resettings and save time and chances of making mistakes, especially when you're testing more than one tube of the same type. For example, the newer Eico 667 charts list for the 12AX7 two different setups to test the two triodes, but the older Eico 666 12AX7 listing (12.6 7, 93 4512145161 2,4 2,3,7,8 1,6 ) goes alot faster. I can test a batch of them in a fraction of the time.

Ron Reeland sent me this schematic showing where to break and make the conections for the plate current mod.When choosing the banana jacks,or whatever type you decide on,make sure to take in to account,their overall height as installed in the panel.I mention this because when you are not using your tester with the jacks in use,you will have to have a jumper in place,obviously.

I chose to use three-way banana jacks,and with a standard jumper in place-I can't close the lid.Sooooo,I have to un- screw the binding knobs and insert a steel pin as a jumper(with an insulated end).That's all I had,so I used them.

Im so happy with my Hickok 752A. Set up the test, push a button to read the meter and then push another button for the other half. Bing, bang, its done

Carl

Mike C. and Ron Reeland...... AWESOME mod for direct plate current measurement.

I'm doing it. Going to shop around for the best jack solution though.... I'm not sure what you meant by the "3-WAY BANANA PLUG"..... I'll start lookin' around......

Anyway.... great action, man!

So I guess the practical application of that measurement point is:

You can dial-in the tube tester's plate and grid voltage settings until you get a plate current displayed on your multimeter that corresponds to the ideal current on a specific tube's data sheet

Is that a correct understanding of that modification?

You are corrrect,that's what the mod is for.I just wanted to do it to satisfy my curiosity-to see just how bad a whipping some tubes really get.Then I just started going through all of the addendums and updates and compared results.Like I said,some tubes they eventually found reasonable settings for,some they never really did.

But,I also have to be carefull about jumping to conclusions and caling some tests invalid.I do not have a stock of NOS tubes to do my testing with.I wish I did,but I can't afford it.All of my tubes are used.Some of the data you can be sure is wrong,when the plate current reading is 5 and 6 times what the tube data books say is average, and the Eico's meter is reading in the replace area.That just ain't right.

A three way binding post is a universal type that accepts banana jacks,probe tips through a hole in the center post,or you can wind a wire around the post and turn the top knob down to bind it..They're nice rigs,but stand kind of tall for this application.

I installed mine in the area of the panel mounted fuse.I relocated the fuse underneath,using a fuse block to mount it to the fame that supports the power transformer.I used the vacant hole for one of the binding posts and made sure to use standard spacing in locating the other next to it.

Hmmmm, interesting idea about relocating the fuse underneath.

I think I'll look for some kind of banana jacks that come on a plate of something.... I saw a really cool dual shorting plug that would conveniently tie the jacks together when you don't wanna plug in your meter.

Thanks again for some great ideas...... I frequently post in several other guitar related forums' amp sections.... this forum has had the most positive solutions to my questions....

Excellent food for thought. (^_^)

Hey MIKE C.,

I sent you a PM regarding that photo of the EICO Plate Current Mod schematic......if you could send me an email with a higher resolution file, it would be appreciated. I'm having a hard time reading some of the schematic details.... just want to make sure I'm cutting the right wires, because it's like a rat's nest under the hood.

Looks like it's a brown wire connected to some Plate switch? The number 4 position? As in the Lever position 4?

Anyway, any insights would be appreciated. I bought a cool dual banana plug jack that can be shorted with a dual shorting plug, if need be. Now I just have to find a good place to mount it.

OK gang...... I got some private messages from MIKE C. and RON REELAND recently concerning the modification to my EICO 667, to allow plate current readings when pulling the MERIT test lever.

I was able to neatly install a dual banana jack into the area directly below the roll chart windows.... right in the middle. It clears the chart roll and there's enough space to route wires from the jack pins to the MERIT lever terminal for PLATE and the #4 PLATE position on the multiple lever buss.

I removed the original brown colored wire that originally connected that MERIT lever terminal to the multiple lever buss, for neatness.

By inserting my DMM probes into the banana jacks, I can simultaneously do the individual MERIT tests on the tube tester AND read the corresponding plate current on my DMM in milliamps!

This really provides another important piece of the equation when trying to develop your own realistic tester settings for a tube. I believe it allows you to tweak your EICO Grid and Plate knob settings so you achieve an ideal plate current close to the tube data sheet maximum plate current spec.

I feel a lot better about the safety to the tube when using settings derived this way..... and although the EICO may not push a tube to it's maximal real world plate voltage, etc.... at least now you can get close to providing a current load that approximates spec.

This added piece of a tube's operation characteristic makes rating tubes in this type of tester a better proposition. Have any other people done this modification and use the plate current to hedge your tube settings?[color=red][/color]

For what it's worth (I have not played around with this): if you test a tube at its normal operating current, you know you have at least that much emission, but no more. There ought to be lots of reserve when the tube is new. I would expect emission testers to run higher than Gm testers, to be able to check this reserve.

If I were trying this, I would start with a working Jackson 648 or a Precision and see what current it uses. I wouldn't trust the Eico data. Eico sold to hobbyists while Jackson and Precision aimed for repairmen.

Hey Alan,

That's exactly why I started this thread...... The EICO data is just suspect enough for you to do your due diligence and investigate your own settings......

There are no EICO chart specs for current...... the modification I did allows you to actually measure the plate current milliamps in real time, with your DMM.

The only thing about reading the current and comparing to a tube manual is the tube tester is using half wave rectified DC sent to the meter while the specs in the manual would be pure DC. you might come up with a fudge factor like .707 for the reading. Then again it depends on the type of meter and how it reads half wave pulsating DC.

Hi Lou,
In the Eico manual,they specify that you use 2/3 of the DC value listed in the tube data sheet for the plate voltage setting("v" lever).Does this sound reasonable to you?Glad to have your input on this subject,thanks.

Hi Alan,
Your suggestion about using a Precision for comparison is a good one,and I have been doing just that for quite a while(model 912).The interesting thing is,some of the results I get from the Precision are just as kooky as from the Eico.

The 6C8g comes to mind as an example.Tube data sheet specifies about 3ma of plate current,if I remember correctly.The Eico was reading my tube in the replace range,the Precision,very high in the good range.Of course,I assumed the Eico was in error.However,I found the plate current reading on the Precision to be around 20 ma,and I think the Eico was reading just about 1ma or so.I think the Eico is slightly more believable in this case.The tube was out of an ancient guitar amplifier,and was quite well used.

I believe I put a call out on the ARF for someone with a Jackson 648 to do some comparison testing,but it didn't spark any interest.Thanks much.

Part of the problem with emission testers is that no one but the tube maker knew what full emission was. And there's no guarantee that different makers used the same spec. For instance, the 6SN7 was a popular sweep tube in TV sets, but it was used in pulse mode and required a lot of emission. Some makes were better than others, even though they all met the tube-manual spec for normal amplifier service.

One of my older amps, a 1948 Gibson BR9, uses a 6SN7 as an octal preamp tube....... the tone is sweet warm and full. That, coupled with a couple of 6V6GT's, and you have low gain sweetness that guitar players yearn for.

Thanks for everyone's insights...... little constructive comments add up to a tribal knowledge that pushes the envelope forward.... digging it a lot. (^_^)