Testing voltages

[ecir38]

I put together these so I would have just one paper to deal with and thought I would share.





In the past I have just left the speakers and the inputs from the preamp hooked up when checking voltages. I would like to be setup to be able to do this on the bench. Wondering what ya'll are using as dummy loads. I know we are dealing with less than 10 watts but it would be nice to have something that would handle more.

Just to clarify where in the manual it says "shorted input, no signal". Would connecting one lead of a rca cable from the left input to the right input be what this is saying?

[ashok]

In the past I have just left the speakers and the inputs from the preamp hooked up when checking voltages. I would like to be setup to be able to do this on the bench. Wondering what ya'll are using as dummy loads. I know we are dealing with less than 10 watts but it would be nice to have something that would handle more.

Just to clarify where in the manual it says "shorted input, no signal". Would connecting one lead of a rca cable from the left input to the right input be what this is saying?

Thanks for the pictures, with the voltage readings. Should be useful.

Shorted input would be shorting the center pin of the RCA jack to the shield of the RCA jack. In other words, ground the input to the amp on each channel. I bought a cheap pair of RCA plugs at Radio Shack, and simply soldered a jumper between the center pin and the shield.

As for dummy loads, I use these Radio Shack resistors.

Hope this helps.

[ecir38]

Shorted input would be shorting the center pin of the RCA jack to the shield of the RCA jack. In other words, ground the input to the amp on each channel. I bought a cheap pair of RCA plugs at Radio Shack, and simply soldered a jumper between the center pin and the shield.

Thanks for the clarification, that should be easy enough.

[ecir38]

ashok, the shorted inputs worked great, thanks.

Posting this to show the differance in voltages between solid state and rectifier tube. I think everything looks ok, if not let me know.


I have this created in excel, if anyone wants a copy shoot me a email.

[Shannon Parks]

Everything looks right on. Is your cathode resistor network 900 ohms? Hmmm - I guess those 300Bs are biased A-OK.

If you don't mind, I would be love to post that Excel doc in the file section. Quick handy!

[ecir38]

Everything looks right on. Is your cathode resistor network 900 ohms? Hmmm - I guess those 300Bs are biased A-OK.!

Yes with three 2.7k's. I am kinda mixed on your comment, do you think this OK? I have been using it like this for awhile with the SS and tube with no problems.

If you don't mind, I would be love to post that Excel doc in the file section. Quick handy!

I will email it to you.

[Shannon Parks]

I will email it to you.

Thanks!

[EWBrown]

I've been using the non -nductive 8 ohm, 10 watt resistors from Parts Express as dummy loads. For the GSG, with its lower power levels, 10 ohms 2-5 watts is more than good enough.

If I need full power tests on the "big amps" then I have some 8.5 ohm, 150 watt "aluminum heat sink" power resistors that I got on the cheap at Eli Hefron's about 35 years ago... These have a slide tap, so I can set for lower resistance if needed for 4 and 6 ohm tests.

"8 ohm" speakers aren't actually 8 ohms across the entire audio spectrum, so the resistors don't have to be super-precise...


(ramble mode on)

Eli's was a electronic and equipment surplus seller in Cambridge Mass, which literally used to price and sell stuff by the pound (and by the ton) , and even individual item prices were less than dirt cheap. Unless the 3rd or 4th generation of Hefron's have taken over , it is probably long gone...

It was one of my favorite hangouts in the late 600s and early to mid 70s,
and living about a mile away was a bonus, as well... Yellow_Light_Colorz_PDT_03

It's unique feature that it was fully owned and operated by two brothers, named Bennie and Jay, and the usual practice was to bring your goodies to one and ask him the price, then wait a few minutes, and ask the other guy. Whoever gave teh best (lower) price was the "winner". Either they never caught on, or else they didn't care.

The other trick that I learned (apparently not to their knowledge) was their "secret alpha-numeric code" of which they would mark items with seemingly random large block letters in chalk or wax crayon.

It didn't take me too long to realize that the particular combination of letters spelled the word "REPUBLICAN", and R stood for 1, E for 2, and so on, with N standing in for zero. So, knowing their own cost was an extra "lever" in dealing with them. Yellow_Light_Colorz_PDT_03

FWIW, some hardware stores and others still use similar codes, Ace and Tru-Value in particular. Go and have some fun playing "codebreaker"...

That was before the days of the hamfests and swapfests that are more the normal standard of today's times and usually have even lower prices and more to choose from.

(ramble mode off)

/ed B in NH