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 Post subject: Re: Eico 147A question.
PostPosted: Sep Thu 07, 2017 11:06 pm 
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Make sure the cathode resistor on the 6AQ5 is still 330 ohms, and also replace the .025 uF cap on the grid if it is wax paper type part.

Pete

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 Post subject: Re: Eico 147A question.
PostPosted: Sep Fri 08, 2017 5:32 am 
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from different positions trying to get everything.


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Fri 08, 2017 5:36 am 
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Peter Bertini wrote:
Make sure the cathode resistor on the 6AQ5 is still 330 ohms, and also replace the .025 uF cap on the grid if it is wax paper type part.

Pete


thank you Pete, I replaced with old 330 with a new 2w (all i had) metal film one, and all the old caps except for the ceramic disk's have been replaced, i also replaced the "gain" pot because it had been burnt badly when i got it. i will have to check and see what i put in there, but i know the gain knob does work now.


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Fri 08, 2017 5:40 am 
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stevebyan wrote:
kk4msa wrote:
getting over 400 out on pin 7 on the 6x4, I'm getting 317ac on pin1,nothing on pin 6 with tune in, but with the tube out, I'm getting 320 Ac on 6.


kk4msa wrote:
well, i have checked everything, i went back through the manual step by step, everything is correctly hooked up. the center tap on the transformer is connected to ground as per manual, im still getting the same voltages310-320vac on pin 1 and 6 of the 6x4, 400+ vdc pin 7,

So you are no longer getting 0 volts on pin 6 of the 6X4 when the tube is in?

It sure sounds like the transformer center tap is connected to pin 6 of the 6X4 and the other end of the winding is connected to ground, or something is shorting pin 6 of the 6X4 to ground.

How did you determine that the center tap on the transformer is connected to ground? An ohmmeter measurement, or did you trace the wiring?

At this point I think we need to see a good close-up photo of the wiring to the 6X4 tube socket.


i was getting 0 on pin 7, im getting 306vac on pin 6.


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Mon 11, 2017 12:54 pm 
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The solder joint between the center tap (wire with the red tracer) and the ground lug on the tube socket looks faulty. Remove the old solder with solder wick or a solder sucker, then re-solder it.

Perhaps the transformer is an incorrect replacement with an excessively high voltage secondary?

With the 6X4 rectifier removed, what is the AC voltage between pins 1 and 6?

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 Post subject: Re: Eico 147A question.
PostPosted: Sep Wed 13, 2017 7:32 am 
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Between 1 & 6 is 318vac. It has the 30023 marked transformer installed. I couldn't find a number in the manual.


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Wed 13, 2017 6:16 pm 
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kk4msa wrote:
Between 1 & 6 is 318vac.

and
kk4msa wrote:
im still getting the same voltages310-320vac on pin 1 and 6 of the 6x4

These two measurements conflict. With a single center-tapped transformer winding, you can't have ≈300 VAC between center tap (circuit commont) and pin 1 of the 6X4, center tap (circuit common) and pin 6 of the 6X4, and between pin 1 and pin 6 of the 6X4. Or did I misunderstand the second quote above - were you measuring between pin 1 and pin 6, rather than from circuit common to each pin?

Let's repeat these measurements carefully, with the 6X4 tube pulled. Measure between circuit common and pin 1, circuit common and pin 6, and between pin 1 and 6.

When you connect to circuit common, are you connecting to the chassis or to the ground lug on the tube socket?

Have you resoldered that connection between the transformer center tap and the ground lug?

What are you using for a meter? If it is a DMM or a VTVM, do you have a VOM you can use instead, or can you put a 100K ohm resistor in parallel with the meter, so we can be sure that you are not reading capacitively-coupled "phantom" voltages?

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 Post subject: Re: Eico 147A question.
PostPosted: Sep Wed 13, 2017 7:40 pm 
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across pins 1 and 6 i get 640vac, from common to each pin is about 320vac.
i used the chassis as ground.
i am using a peak reading 6k count per second dmm, i have a vtvm, but haven't used it on this, just been using the digital multi.
i have resoldered all pins on the 6x4 and aq5 as well as the center tap ground.


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Wed 13, 2017 8:26 pm 
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kk4msa wrote:
i am using a peak reading 6k count per second dmm

So you are reporting peak AC voltages rather than RMS values? Most meters, even if they are average-reading rather than true-RMS-reading, report RMS values. Are you sure your DMM is reporting peak values for AC?

A reading of 320 volts peak AC on pins 1 and 6 of the 6X4 is equivalent to 226 RMS AC, so your HV AC voltages would actually be close to what the manual specifies, if you are really measuring peak AC volts.

Is your meter also reporting peak DC rather than average?

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Last edited by stevebyan on Sep Thu 14, 2017 5:37 am, edited 1 time in total.

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 Post subject: Re: Eico 147A question.
PostPosted: Sep Wed 13, 2017 9:45 pm 
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Quote:
peak DC rather than average


?????????? ;-) <wry grin> No peeking now ....


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Wed 13, 2017 10:24 pm 
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OK, ok, "peak voltage of the sum of DC plus AC ripple".

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 Post subject: Re: Eico 147A question.
PostPosted: Sep Wed 13, 2017 10:46 pm 
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LOL I knew whatcha meant ... couldn't help myself :evil:


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Fri 15, 2017 9:02 am 
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It reads the same thing as my old bench b&k 2831a, so I'd say average. I use both depending on the amount of junk on the desk.


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Mon 18, 2017 2:30 am 
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kk4msa wrote:
It reads the same thing as my old bench b&k 2831a, so I'd say average. I use both depending on the amount of junk on the desk.

OK, then the transformer doesn't match the manual. Does it look like a replacement?

You'll need to find a replacement transformer that is more compatible with the original.

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 Post subject: Re: Eico 147A question.
PostPosted: Sep Tue 19, 2017 1:18 am 
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It does not look like a replacement, all of the wire coating matches the other 2 in there. Also they all have the number 32003 on them. I would bet that's the original transformer, so that 300+ volts on 1 and 6 is to much, what would make a transformer go bad and raise the Ac several volts? Man I'm sure it will take a min to find one, I see some listed on eBay, bit judging by the size in the pic, it's one of the others in there, not the HV supply. Since it seems to run the 310v steadily, could that be dropped without being more work than its worth?


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 Post subject: Re: Eico 147A question.
PostPosted: Sep Tue 19, 2017 4:00 am 
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kk4msa wrote:
what would make a transformer go bad and raise the Ac several volts?

Pull the 6X4 rectifier, leave the rest of the tubes in, plug it in, turn it on, and measure the filament voltages. Are the filament voltages also 40% high?

If so, does the transformer heat up to the point where it is uncomfortable to touch?

If so, then perhaps there are some shorted turns in the primary, possibly caused by running it with leaky filter capacitors.

kk4msa wrote:
Since it seems to run the 310v steadily, could that be dropped without being more work than its worth?

I don't think so. Especially if the transformer overheats.

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 Post subject: Re: Eico 147A question.
PostPosted: Sep Tue 19, 2017 8:17 am 
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As to the transformer measurements, the T147-A is rated 110-125 VAC 50/60 Hz.
Core and turns ratio are not valid, because of the need for a working benchmark.
Quibbling about marginal voltages is futile, in my opinion.

Here is another test. Power consumption.

(I own about ten T147-A tracers, classroom set.)



With all the tubes in their sockets, switch the T147-A output to wattmeter function.

Tape up the pins on the end of the line cord.

Now make up a line cord with a two pin plug on either end. Make sure the plug on one end
will fit the front panel receptacle J11.

Read page 3 of manual.


Relax.


Now plug one end of the double male line cord into J11.

Now plug the other end into the wall socket.

Measure the wattage draw of your T147-A.

Compare it with nameplate wattage.

Note it is calibrated for 117 VAC.

After you have completed the test, cut one of the plugs off the double male cord. Tape
up the free wires.

The above is confidential. It may only be used for winning bar bets.

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