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Post subject: Re: Questions and Help with 68 PR
Posted: Mon Sep 24, 2018 2:39 pm
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Also while poking around I discovered a leg floating on the center .01 disc cap for the tremolo, I soldered it back inImage But I am curious, that Temple 25+25 uf 25vdc was "DOA" short it had continuity on both sides, I believe one side is for the Vibrato and the other is for the Reverb mix. Now this was the only cap that was shorted, the others were just way out of tolerance, but still worked.
Question? Is it possible that the .01 disk cap shorted them out or would it be something else other than age. I also do not think fender used theses Temples, so there must have been an issue prior, and I can't find anything about these caps when google searching either
mud


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Post subject: Re: Questions and Help with 68 PR
Posted: Mon Sep 24, 2018 5:46 pm
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mud wrote:
I also do not think fender used theses Temples, so there must have been an issue prior, and I can't find anything about these caps when google searching either
mud


Fender used those. Here's one example.

UN

https://www.gbase.com/gear/fender-princ ... erb-1968-3


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Post subject: Re: Questions and Help with 68 PR
Posted: Mon Sep 24, 2018 7:18 pm
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upnorth2 wrote:
mud wrote:
I also do not think fender used theses Temples, so there must have been an issue prior, and I can't find anything about these caps when google searching either
mud


Fender used those. Here's one example.

UN

https://www.gbase.com/gear/fender-princ ... erb-1968-3

Interesting, makes me feel even better about this PR, as it did not appear to have been touched until I got my hands on it. When I saw those caps I had no idea, thought they were a repair, but at the same time they fit so perfect and the solder job looked the same on all the eyelets, so I was confused....
Thanks for straightening that out for me. I see I also have the 10J5 Speaker and according to your link its better than the 10J4
mud


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Post subject: Re: Questions and Help with 68 PR
Posted: Tue Sep 25, 2018 3:15 am
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Location: Coastal Bend, Tx.
The AA764 does look like the right layout for your amp, in the photo I couldn't tell/see the year/date but only noticed the tube difference from what I have available. Glad you got most of the updates completed over the weekend. On the trem caps, maybe the bias cap went out and the disk cap was lifted to test or to cut the signal to the trem.

As far as starting up, you could always test the power transformer, negative bias supply, power switch, fuse, lamp, power outlet/new 3 prong and heater voltages to all tube sockets with the amp unloaded (no tubes). You will only be checking AC voltages except for the -bias diode output.

I always start up this way, then follow w/ the rectifier only, then the output tubes, then PI and pre amp tubes. Helps me to find issues easier w/in circuits. Some high voltage anomolies occur until all tubes are loaded but that is just a display of what max voltages may be seen on circuit in the event of an actual tube short.


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Post subject: A New Questions with my 68 PR
Posted: Sun Oct 07, 2018 2:24 pm
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I changed all the e Caps and the power rail resistors and the 2 EH 6v6gt I ordered came in I put in the tubes and plugged it into the bucking transformer 115VAC played a little had reverb and weak vibrato, turned off put in my bias probe and saw 45ma, plate voltage 430vdc Turned it off opened it up checked that 100K resistor that wants only 5% tolerance and it measured 128K changed it out,and using my probe again I measured 21.9ma on V6 and 20.7 V5, much better, but I wanted to make sure I was within the parameters of my amp so I remeasured, using the OT Resistance and Voltage Drop method and my results were like this:
V6) Resistance from pin 3 to pin 8, half of the transformer, 155.3ohm, than I measured Voltage Drop---3.39. Plate current is Volts over Resistance so that equaled 21.8ma
V5) Resistance from pin 3 to pin 8, half of the transformer, 154.9ohm, than I measured Voltage Drop---3.28. Plate current is Volts over Resistance so that equaled 21.1ma
Than I measured Plate voltage
V6) 406.9VDC (PV)(PC)=PD Plate Dissipation 409.9 X .0218 = 8.870 W
V6) 407.5VDC (PV)(PC)=PD Plate Dissipation 407.5 X .0211 = 8.598 W
So now with this info my new Question is:
I keep reading and I keep seeing that EH 6v6GT are 12Watt rated and than I read else where they are 14Watt rated.
So when I look Plate Dissipation for 70% of 12W I get 8.4W
Than I look at Plate Dissipation for 70% of 14W I get 9.8W
So my question am I running too Hot or too Cold
Question 2: Right now I am running a new production Ruby 5AR4 If I put a NOS Rectifier tube in will that have a big change on the EH 6v6 parameters, a Mullard GZ34 came with it.
I have some older RCA and Sylvania 6v6 but none that are matched so at some point I will go find a set of RCA or GE 6v6 and use the Mullard
Thanks
mud


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Post subject: Re: Questions and Help with 68 PR
Posted: Mon Oct 08, 2018 6:59 am
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Image

Whoa! Love the vintage 100-watt iron (is that an American Beauty?) and the Kester Radio Solder can!

:)


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Post subject: Re: Questions and Help with 68 PR
Posted: Mon Oct 08, 2018 7:16 am
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BMW2002Ti wrote:
Image

Whoa! Love the vintage 100-watt iron (is that an American Beauty?) and the Kester Radio Solder can!

:)

I believe it is and the Kester is full of it's original solder. Found it about 3years ago for $5.00, it came with the box and I think I was the first to use it as it had no heat marks that are there now on it
mud


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Post subject: Re: Questions and Help with 68 PR
Posted: Mon Oct 08, 2018 7:45 am
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Location: Coastal Bend, Tx.
To hot or to cold? How does it sound and does it breakup when you would expect it to.
IMO, if you want to see what a higher PV would be like; using a higher input voltage is the easiest test(take the bucking x-trns out of the mix). A different rectifier tube will either be more or less efficient, plug and test is the only reliable method.
Whats your negative grid voltage V5&6 P5? should be -34...
Also on the tubes, run what ya brung. The EH's & Ruby are good to use as initial testers(inexpensive to replace). Now you know the circuit is good to go, I'd put in the Mullard and any of the two older 6v6's and re-check your bias & wattage numbers.

+2 on the old iron :)


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Post subject: Re: Questions and Help with 68 PR
Posted: Mon Oct 08, 2018 9:25 am
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sfceric64 wrote:
To hot or to cold? How does it sound and does it breakup when you would expect it to.
IMO, if you want to see what a higher PV would be like; using a higher input voltage is the easiest test(take the bucking x-trns out of the mix). A different rectifier tube will either be more or less efficient, plug and test is the only reliable method.
Whats your negative grid voltage V5&6 P5? should be -34...
Also on the tubes, run what ya brung. The EH's & Ruby are good to use as initial testers(inexpensive to replace). Now you know the circuit is good to go, I'd put in the Mullard and any of the two older 6v6's and re-check your bias & wattage numbers.

+2 on the old iron :)

Good points all around, it does sound very good ( louder also than I thought for a 12watt amp) at Volume 4.5 I get a slight break up and at 6 it rips.
I will check on the negative grid voltage when I open it up again, I guess I should than pin them all and wright it down.
I will put in the Mullard and see what 6v6's I have are the closest match, and go from there.
Thanks, I guess I read, and do research about these thing and some times there are too many conflicting points that I just want to scream, especially when it come to the bias measurement, some say Oh you can't go above 19ma in a PR, but my numbers with the EH and Ruby seem in the ball park, so when I do some experimenting with the tubes I own, I will let the numbers and my ears be the judge
Thanks for your input
mud


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Post subject: Re: Questions and Help with 68 PR
Posted: Tue Oct 09, 2018 7:55 am
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Location: Coastal Bend, Tx.
Glad to hear your up and running, Mud. You're good to go w/405- 415PV and .019-.022ma w/ 12 watt 6v6's.


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