Calling Rockstah - 1959 HW to 12xxx series spec

[toner]

vkaxeman,
Regardless of the meter in question, you always want it set to VOLTS (2dcv, 200mV, whatever) when testing bias via the 1 ohm resistor method. Forget about amperes, mA, etc. settings for this purpose.

This amp better be absolutely killer for the amount of trouble you've gone through!!! You're detailed posts will likely help a lot of people though.

[rockstah]

the 1 ohm resistors u installed on the output tubes do in fact measure 1 to 1.2 ohm?

I have 4 more of these not installed yet. I will measure one to confirm.

u can take your meter, one lead to the chassis and one lead to the tube socket side of the 1 ohm and measure them.

[vkaxeman]

Here is one of the Bias Resistors measured on DMM1 (Exetech):

Here is the same Bias Resistor measured on DMM2 (Cheapy):

Here are pics of the Electro Harmonix Tubes:



So this was a total waste of time. The readings with the EH EL34's are worthless, (definetly the tube in V4):

With Bias pot all the way down/minimum:

V4 = 1.60ma using Exetech set on 20ma
V4 = 1.48ma using Cheapy DMM set on 20ma

V5 = 0.08ma using Exetech set on 20ma
V5 = 0.07ma using Cheapy DMM set on 20ma

V6 = 0.05ma using Exetech set on 20ma
V6 = 0.03ma using Cheapy DMM set on 20ma

V7 = 0.16ma using Exetech set on 20ma
V7 = 0.14ma using Cheapy DMM set on 20ma

With Bias pot turned 1/4 way up to Max:

V4 = 2.01ma using Exetech set on 20ma, set on 2vdc = .024
V4 = 1.89ma using Cheapy set on 20ma, set on 2vdc = .023

V5 = 0.18ma using Exetech set on 20ma, set on 2vdc = .003
V5 = 0.16ma using Chepay set on 20 ma, set on 2vdc = .001

V6 = 0.12ma using Exetech set on 20ma, set on 2vdc = .002
V6 = 0.11ma using Cheapey set on 20ma, set on 2vdc = .001

V7 = .032ma using Exetech set on 20ma, set on 2vdc = .004
V7 = .028ma using Cheapy set on 20ma, set on 2vdc = .003

[vkaxeman]

vkaxeman,
Regardless of the meter in question, you always want it set to VOLTS (2dcv, 200mV, whatever) when testing bias via the 1 ohm resistor method. Forget about amperes, mA, etc. settings for this purpose.

This amp better be absolutely killer for the amount of trouble you've gone through!!! You're detailed posts will likely help a lot of people though.

Ok say your saying that the readings that I was previously getting with the JJ EL34's below when measuring set at 2vdc mean that my bias is way cold and that I should not be using the ma readings????? If this in fact true, then the JJ's are really pretty closely matched - .006, .004, .005, .005 and I need to crank up the bias pot?

____________________________________________________________
JJ EL34 tube's still in the amp, have not removed them yet.)

With the Exectech set to 2 volts dc, black lead in Com jack and Red Lead in the Volt/Ohm/Hertz Jack as per the manual:

V4 = .006: my previous reading with my manual range cheapy on 2vdc was .005

V5 = .004: my previous reading with my manual range cheapy on 2vdc was .003

V6 = .005: my previous reading with my manual range cheapy on 2vdc was .004

V7 = .005: my previous reading with my manual range cheapy on 2vdc was .004

With the Exetech set on 20ma dc, black lead in Com jack and Red lead in ma/ua fused 200ma Max Jack as per the instruction manual:

V4 = 0.47ma: my previous reading with my manual range cheapy on 20ma was 0.45ma

V5 = 0.25ma: my previous reading with my manual range cheapy on 20ma was 0.26ma

V6 = 0.37ma: my previous reading with my manual range cheapy on 20ma was 0.38ma

V7 = 0.37ma: my previous reading with my manual range cheapy on 20ma was 0.38ma
____________________________________________________________

I would sure like to resolve this issue before this thing hits page 100.

[bluze81]

Have you fired this amp up since installing the Dagnall clone output transformer and put an ear to it yet?

[vkaxeman]

Have you fired this amp up since installing the Dagnall clone output transformer and put an ear to it yet?

Yeah that happened way back. Not sure how many pages and posts. Been dealing with this bias issue and I am writing a novel.

[toner]

Ok say your saying that the readings that I was previously getting with the JJ EL34's below when measuring set at 2vdc mean that my bias is way cold and that I should not be using the ma readings????? If this in fact true, then the JJ's are really pretty closely matched - .006, .004, .005, .005 and I need to crank up the bias pot?

Your latest bias readings with the two different meters are very close.

The reason I said to use the volt settings is because some meters are more accurate with low voltages than low current readings (at least in my experience). Technically, the reason the 1 ohm resistor bias method works is because it gives you the equivalent mA current value when reading mV across the resistor (Ohm's law).

[vkaxeman]

Ok, so I put the JJ EL34's back in.
Cranked the Bias Pot all the way up/maxed:

Here are the readings using both meters, (Exetech and the Cheapy), both set on 2 volts dc:

V4 = .019 Exetech DMM
V4 = .018 Cheapy DMM

V5 = .013 Exetech DMM
V5 = .012 Cheapy DMM

V6 = .017 Extech DMM
V6 = .016 Cheapy DMM

V7 = .017 Extech DMM
V7 = .016 Cheapy DMM

V5 still looks a little on the low side but usable.

Is this the correct way to measure the bias? So I need to put the 33k resistor in? Will the 33k resistor allow me to get the readings up to .035 to .041 range?

[vkaxeman]

the 1 ohm resistors u installed on the output tubes do in fact measure 1 to 1.2 ohm?

I have 4 more of these not installed yet. I will measure one to confirm.

u can take your meter, one lead to the chassis and one lead to the tube socket side of the 1 ohm and measure them.

Checked em all in the amp, all 4 read 1.4 ohms. This OK?

[vkaxeman]

Gotta go for the night but tomorrow night I will put the 33k resistor back in for the bias resistor and see if I can get the tubes in the .035 to .041 range using 2 volts dc setting on my Multi-meters.

Thanks Guys!!!!

[Coot Boy]

Rightio then, it's obvious now that you have had the f###ing bias pot turned down to bugger all and reading from the 20Ma setting, change the resistor to 33K and you should get it up to where you want it. When you said
" I double checked and it is labeled 20ma and that's where I have it with the latest readings. When I move it to the next option which is 200ma I get readings like 00.6 00.6 00.5 00.3?" These readings are consistant with the 2dcv readings you were getting up until when you finally turned the bias pot UP.

[vkaxeman]

Rightio then, it's obvious now that you have had the f###ing bias pot turned down to bugger all and reading from the 20Ma setting, change the resistor to 33K and you should get it up to where you want it. When you said
" I double checked and it is labeled 20ma and that's where I have it with the latest readings. When I move it to the next option which is 200ma I get readings like 00.6 00.6 00.5 00.3?" These readings are consistant with the 2dcv readings you were getting up until when you finally turned the bias pot UP.

Yep, I'm going thru "Digital Multi-Meters 101" and everyone's taking the class with me. LOL Sorry about that. Gotta learn somehow.

[rockstah]

Ok, so I put the JJ EL34's back in.
Cranked the Bias Pot all the way up/maxed:

Here are the readings using both meters, (Exetech and the Cheapy), both set on 2 volts dc:

V4 = .019 Exetech DMM
V4 = .018 Cheapy DMM

V5 = .013 Exetech DMM
V5 = .012 Cheapy DMM

V6 = .017 Extech DMM
V6 = .016 Cheapy DMM

V7 = .017 Extech DMM
V7 = .016 Cheapy DMM

V5 still looks a little on the low side but usable.

Is this the correct way to measure the bias? So I need to put the 33k resistor in? Will the 33k resistor allow me to get the readings up to .035 to .041 range?

thats it man. and yes put that 33k in there. - reading the bias with 2dcv setting and its all good.

with 400dcv on the plates you want to bias it up to .037 = 37mA .

so check the b+ once you get into bias range and re calculate reset bias.

so somewhere between 60 and 70 MPD

.60 X 25 = 15/ voltage on plates = bias setting
.70 x 25 = 17.5/ voltage on the plates = bias setting

.60x25=15/400dcv = .037 = 37mA
.70x25=17.5/400dcv = .043 - 43mA

set it at 37mA and turn it up and listen for the sweet spot but don't go past 43mA.

i usually leave it at 60 percent with an amp thats being dimed but u can use your ear as well.

[thousandshirts]

Yep, I'm going thru "Digital Multi-Meters 101" and everyone's taking the class with me. LOL Sorry about that. Gotta learn somehow.

You are doing AWESOME. Hang tight, and before you know it, you'll be done.

[vkaxeman]

After removing the 47k bias resistor and installing a 33k resistor in it's place, here's the best I could do in Biasing the JJ EL34's by numbers (not by ear):

Multi-meter on 1000 volts DC:
B+ Voltage = 406 volts dc ( same reading on Pin 3 of all Power Tube Sockets)

Multi-Meter on 2 volts dc:
V4 = .043 volts
V5 = .034 volts ( This tube is still running low )
V5 = .040 volts
V6 = .039 volts

Bias was set based on:
Low Number: .60 X 25 = 15/ 406 (voltage on plates) = 0.036946 (bias setting) which is really 0.037 but rounded down would be 0.036

High Number: .70 x 25 = 17.5/ 406 (voltage on the plates) = 0.043103 (bias setting) which rounded down would be 0.043

Calculations looks like:
.60x25=15/406dcv = 0.036946 = .037 volts = 37mA
.70x25=17.5/406dcv = 0.043103 = .043 volts = 43mA

With the 33k resistor the Bias pot ended up about 3/4 the way up to MAX.

As you can see the tube in V4 is at the high end of the range and the tube in V5 ( the one that has been reading low all along) is still reading low and did not make it to the desired Low Number. I will contact George to see about getting a replacement for the tube in V5. The boxes that they came in have numbers on them so maybe he can find me a match based on that. I hope.

MP3's coming tomorrow.