Thanks for the tip, but there is actually a bit of clearance there because the bolt slots are raised from the surface where the tube seats.
I think I may have made a mistake with rotational alignment Of the sockets, I put all mounting bolts left to right of the chassis. I think I should have turned certain ones front to back based on their pin out.
I think I may have made a mistake with rotational alignment Of the sockets, I put all mounting bolts left to right of the chassis. I think I should have turned certain ones front to back based on their pin out.
What gauge wire is suggested for the voltage & amperage of this project? I was hoping to have enough Left over when trimming the leads from the transformers but I realize that it won’t leave me much to work with. I like the idea of authenticity of using the lacquered cloth wire that Antique Audio Supply sells, does anyone have any input on that?
I have a question that I am almost certain of but I want to verify 100% with the help of you all. I’ve got a good amount of work done, so I think, and got to R13 located at the ECC99 (I believe) cathode. It shows ONE R13: 330ohm resistor, I just want to confirm this is ONE resistor per half of the tube. One for pin 3 to ground and one for pin 8 to ground. Below is a link to the schematic again with my most current notations:
The Apple-Fire - Schematic with notes
Progress picture:
The Apple-Fire - Current Progress
The Apple-Fire - Schematic with notes
Progress picture:
The Apple-Fire - Current Progress
> lacquered cloth wire that Antique Audio Supply sells
That's bric-brac over a super tough high-rated plastic insulation. Everybody(?) hates it. Hard to strip and tastes wrong.
Hoffman Amplifiers has true cloth wire. While not rated, it has been used in hundreds of tube amp builds without reported problem.
That's bric-brac over a super tough high-rated plastic insulation. Everybody(?) hates it. Hard to strip and tastes wrong.
Hoffman Amplifiers has true cloth wire. While not rated, it has been used in hundreds of tube amp builds without reported problem.
Cool! Thanks for help! Again...
I have ordered all but the 2A3 tubes. Still hoping to hear some feedback on which 2A3 to use for a first. They’re not cheap tubes so I don’t plan to do too much tube rolling for a little while.
I have used Electro Harmonix and Sovtek 2A3s. I liked both of them. They are made for up to 15 Watt plate dissipation.
I have also used JJ 2A3s, and I liked them too. But they are made for up to 40W plate dissipation, and so they are larger diameter glass to dissipate the heat. You need more space between the tubes, and from the tubes to other items on the top of the amplifier.
I do not have any 2A3 amplifiers now. I would like to build them again, but I will use DC on the filaments this time. There are reasons for this, it has been discussed in many other threads on this forum.
I really did enjoy the 2A3 amps I had, they used AC filaments, and others enjoyed listening too; so do build the amp just as you planned.
I have also used JJ 2A3s, and I liked them too. But they are made for up to 40W plate dissipation, and so they are larger diameter glass to dissipate the heat. You need more space between the tubes, and from the tubes to other items on the top of the amplifier.
I do not have any 2A3 amplifiers now. I would like to build them again, but I will use DC on the filaments this time. There are reasons for this, it has been discussed in many other threads on this forum.
I really did enjoy the 2A3 amps I had, they used AC filaments, and others enjoyed listening too; so do build the amp just as you planned.
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This is probably a stupid question, but again I want to understand things in as much detail as I can....
My power transformer has two solid yellow wires and the schematic provided shows “5V” on one and “COMMON” on the other. Does the transformer itself actually have polarity or is the polarity determined by the circuit? Does it matter which wire I use as my common or do I have to test the transformer to find which is the common?
The other secondary windings were center tapped, so that is distinguishable. But maybe I don’t understand how CT’s work...
I need to find some good educational books to learn more about all of this stuff. Anyone have any recommendations?
My power transformer has two solid yellow wires and the schematic provided shows “5V” on one and “COMMON” on the other. Does the transformer itself actually have polarity or is the polarity determined by the circuit? Does it matter which wire I use as my common or do I have to test the transformer to find which is the common?
The other secondary windings were center tapped, so that is distinguishable. But maybe I don’t understand how CT’s work...
I need to find some good educational books to learn more about all of this stuff. Anyone have any recommendations?
Because there is no center tap, and both wires are yellow (verify they are connected together with an ohmmeter) one has to be 5V and the other is the return of the 5V.
Digital Ohmmeters do not like inductance, often autorange-hunt-hunt-hunt. You may have to short the HV secondaryary leads to read the DCR of the 5V winding.
I think it is silly that the manufacturer labeled it that way.
It is 5V from any one of the two yellow leads to the other of the yellow leads.
This winding is meant to be used for the 5V rectifier filament.
Digital Ohmmeters do not like inductance, often autorange-hunt-hunt-hunt. You may have to short the HV secondaryary leads to read the DCR of the 5V winding.
I think it is silly that the manufacturer labeled it that way.
It is 5V from any one of the two yellow leads to the other of the yellow leads.
This winding is meant to be used for the 5V rectifier filament.
It has been an interesting few weeks with the latest developments on the pandemic situation... needless to say this was put to the back burner for a little bit, but I did order a set of Sovtek 2A3’s. I went with the cheaper route just to keep budget while being able to expedite them considering the uncertainty of the effects of the virus on shipping.
I have my Tektronix 2337 oscilloscope out and using for its DMM set on 2k. I am getting anywhere between .6 - 1.6 ohm between the 5v (yellow) wires, regardless of HV secondary being shorted or not.
I am confused by your statement though, about the 5v coming from “any one” of the yellow leads. Are you saying that it does NOT matter which one is applied to which pin on the rectifier tube?
I have my Tektronix 2337 oscilloscope out and using for its DMM set on 2k. I am getting anywhere between .6 - 1.6 ohm between the 5v (yellow) wires, regardless of HV secondary being shorted or not.
I am confused by your statement though, about the 5v coming from “any one” of the yellow leads. Are you saying that it does NOT matter which one is applied to which pin on the rectifier tube?
Yes, that's the nature of AC.
If there happens to be a third wire that's yellow with a black stripe, do let us know.
When you read low Ohms on an Ohmmeter, just the contact resistance, and the variability of that with other wires can cause different readings.
0.6 Ohms might be correct, but only if you include the fact of ohmic connections of both leads and the wires they connect to.
1.6 Ohms would be quite a problem.
A 5V 2.0 Amp rectifier filament would cause a drop 2.0A x 1.6 Ohms = 3.2V
A true winding of 0.6 Ohms is also too much, 2 amps rectifier filament would drop 1.2V.
Zero your Ohmmeter, and try again, make sure the Ohmic contacts are tight to really clean wires. Anything else is an incorrect measurement result (It is if the rectifier filament heats up).
A 5V 2.0 amp rectifier tube filament is 2.5 Ohms when the filament is Hot.
It is much less than that when the filament is cold.
Go ahead and practice, and measure the cold resistance of your rectifier tube.
I do not remember if you have a bleeder resistor in your amplifier.
Poking around when there is no bleeder resistor (or before the bleeder resistor has had time to discharge the B+) is very dangerous.
What is the worst that can happen . . . It is called "The Surviving Spouse Syndrome".
It looks like the schematic in the link of post #1 does have a 330k Ohm bleeder resistor.
Make sure it is there, and that it is not burned out.
Safety First!
0.6 Ohms might be correct, but only if you include the fact of ohmic connections of both leads and the wires they connect to.
1.6 Ohms would be quite a problem.
A 5V 2.0 Amp rectifier filament would cause a drop 2.0A x 1.6 Ohms = 3.2V
A true winding of 0.6 Ohms is also too much, 2 amps rectifier filament would drop 1.2V.
Zero your Ohmmeter, and try again, make sure the Ohmic contacts are tight to really clean wires. Anything else is an incorrect measurement result (It is if the rectifier filament heats up).
A 5V 2.0 amp rectifier tube filament is 2.5 Ohms when the filament is Hot.
It is much less than that when the filament is cold.
Go ahead and practice, and measure the cold resistance of your rectifier tube.
I do not remember if you have a bleeder resistor in your amplifier.
Poking around when there is no bleeder resistor (or before the bleeder resistor has had time to discharge the B+) is very dangerous.
What is the worst that can happen . . . It is called "The Surviving Spouse Syndrome".
It looks like the schematic in the link of post #1 does have a 330k Ohm bleeder resistor.
Make sure it is there, and that it is not burned out.
Safety First!
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I received my new test leads....
When I shorted the contacts together on the old leads *now* I read 3.xx Ohms. With these new test leads, I am still getting 0.3 Ohms. I was really expecting to see closer to 0.00 ohms. Is that typical to have 0.3ohms just from the contact points? Or is there something off with my scope as well?
When I shorted the contacts together on the old leads *now* I read 3.xx Ohms. With these new test leads, I am still getting 0.3 Ohms. I was really expecting to see closer to 0.00 ohms. Is that typical to have 0.3ohms just from the contact points? Or is there something off with my scope as well?
The normal calibration cycle for electronic test equipment is 1 year.
Many military and other government agencies require much of that equipment to be on a 6 month calibration cycle.
If the test equipment passes all of its specifications, then generally no re-adjustments are made, unless a spec is very close to its 'border' value.
Lots of test equipment can go many years of calibrations without re-adjustment.
The first thing to do is find your scope manual, including the DMM manual, and find out if there are instructions that lists an external user adjustment for the Ohmmeter.
The next thing is to check the accuracy specifications, and see if the DMM Ohmmeter is out of spec.
Did you ever get your Ohmmeter across either an AC or a DC a voltage source?
You may have let some smoke out of the circuitry.
I have been making calibrated electrical measurements since 1959.
I have seen a lot of things, but I have not yet seen it all.
Many military and other government agencies require much of that equipment to be on a 6 month calibration cycle.
If the test equipment passes all of its specifications, then generally no re-adjustments are made, unless a spec is very close to its 'border' value.
Lots of test equipment can go many years of calibrations without re-adjustment.
The first thing to do is find your scope manual, including the DMM manual, and find out if there are instructions that lists an external user adjustment for the Ohmmeter.
The next thing is to check the accuracy specifications, and see if the DMM Ohmmeter is out of spec.
Did you ever get your Ohmmeter across either an AC or a DC a voltage source?
You may have let some smoke out of the circuitry.
I have been making calibrated electrical measurements since 1959.
I have seen a lot of things, but I have not yet seen it all.
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