Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => AmpTools/Tech Tips => Topic started by: Justa on April 23, 2009, 10:58:06 am

Title: My Old Analog Meter Died, Need Help Selecting a Replacement
Post by: Justa on April 23, 2009, 10:58:06 am

Finally after 25 years my old analog meter is too screwy to fix.  I am looking for a fairly rugged low cost analog meter to compliment my digital.  The low cost is very important but I want something that is worth having.  What do you folks think, should I be thinking E-Bay old used Simpson 260 or are there other good options today.  I don't have a clue as my knowledge is very dated and that's why I am wondering if the old Simpsons are still a good choice.  I use my meters for many other purposes other than amps and they do get banged around some times.

Thanks

Title: Re: My Old Analog Meter Died, Need Help Selecting a Replacement
Post by: Justa on April 23, 2009, 07:19:58 pm

Found a used 260 Simpson in an extreme rural area I will be driving through tomorrow.  It will be interesting as the gent selling it didn't seem to know anything about it and told me he would have to find out how much to sell it for. 

Does anybody know anything about the series changes on the 260's.  I see that they range from series 2 to series 9 but don't know anything about the changes.

Thanks

Title: Re: My Old Analog Meter Died, Need Help Selecting a Replacement
Post by: tubesornothing on April 23, 2009, 07:22:03 pm

google "simpson meter models"   


lots of stuff

Title: Re: My Old Analog Meter Died, Need Help Selecting a Replacement
Post by: Justa on April 23, 2009, 08:02:14 pm

Wow,
I had tried that earlier but hit the jackpot this time. :)

Here is a link that has everything imaginable on the 260 Simpson series from the 30's to current models.  What the heck else in electronics has lasted that long?  Nothing I can think of.

http://www.simpson260.com/

Thanks Tubes

Title: Re: My Old Analog Meter Died, Need Help Selecting a Replacement
Post by: 69SG on September 08, 2009, 03:08:43 pm

Thanks !!
I just downloaded the manual for my 260-6

Title: Re: My Old Analog Meter Died, Need Help Selecting a Replacement
Post by: PRR on September 10, 2009, 12:54:22 am

> What do you folks think, should I be thinking E-Bay old used Simpson 260

The 260 is a -passive- meter.

On Volts it is 20K/V, which means the 50V range is 1Meg impedance. That can be considerable loading in tube circuits.

A Vacuum Tube Voltmeter (VTVM) has been the bench standard for amplifier-hackers since the late 1950s. VTVMs are usually 11Megs impedance on all ranges.

Note that the "passive" 260 reaches 10Megs on its 500V range. So for higher tube voltages, it can be "as good as" a VTVM. If you read say 90V on the 500V scale, you are working below 1/5th of the scale and have to squint close to resolve better than 5%. However most tube-work is +/-20%, so close squinting is not required.

The 100mA and 500mA ranges are directly useful on tube power stages, and few/no classic VTVMs give you this function (except with external resistors and the Volts function).

If you do the modern custom of using 1-ohm resistors to sense current, neither the 260 nor the classic VTVM will closely resolve 0.046V (46mA, a possible bias target). That's strictly modern digi-meter territory. In the old days, we used 10 ohm resistors to sense current.

The 260's Ohms gets awful cramped above 1 Meg, but most meters do. (Some DMMs don't read over 1.99Meg; the 260 knows "open" from "10Meg".) The 260 easily reads below 1 ohm; many DMMs have an ohm of internal slack and some simply round-down anything less to "0.00".