Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: uki on June 20, 2016, 08:13:44 pm
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Hey guys !
I got this hi-fi monaural amp, couldn't find anything about it on internet, no schematic, not even some mention about it, nothing :dontknow: . The amp does have one socket for reticfier tube, two sockets for power tubes, those were missing, the amp only came with the preamp tubes, 6SL7, 6SN7, EF86, ECC83.
I'm disassembling it to use the parts for a new guitar amp, already figured out the PT wires, and some of the OT wires here what I got so far:
PT primary(see picture):
115v 50cy
PT Secondary:
2x 350v 200mA
5v 4A , 6.3v 5A , CT
OT primary have 5 wires
brown and blue going to pin 3 of the power tubes,
green and black going to 1k big resistor and then to pin 4 of the power tubes,
and red seen to be the center.
OT secondary have 4 wires
black going to ground
red, brown and blue going to 8pin socket which is connected to a 3 way switch.
Here are the impedance between the primary wires I got with the meter only(I did not hook it up on a power source):
brown / red = 150 ohms
blue / red = 170 ohms
green / red = 50 ohms
black / red = 50 ohms
brown / blue = 200 ohms
black / green = 70 ohms
What do you guys think ? Is this OT usable for a guitar amp?
Thanks in advance !
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I am sure you can convert the hifi amp to a guitar amp. You are likely looking at a preamp modification, nothing too serious.
Did you find any numbers on the O/T. With this info you might be able to get info on the specs for the o/t. Post any numbers you find on the O/T. From the O/T, you can back figure what power tubes you directly plug in.
Verify the blue/red ohm readings, your reading appears to be an outlier when combined, I would have guessed from the other readings, it should be about 150 ohms and not 2K.
While there are few guitar amps that use ultralinear trannys, You might want to consider not using the UL taps, those with more experience will likely chime in.
Look at various fender schematics for typical wiring schemes for the input side.
For tone control, look up duncan amps, looking for the tone calculator, it provides a few designs, if you have bass and treble, I am guessing you have a bandaxel tone control.
I am guessing the ECC83 is a PI.
good luck with your project
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To me the first thing to be done is to reverse engeener the amp and draw the schematic
after that to convert it in a guitar amp will be simpler
as general roule
when you have under hand an amp that you want to convert
keep PI - Power Supply - Output Transformer as in the original amp
this will semplify a lot your life
Franco
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OT primary have 5 wires
brown and blue going to pin 3 of the power tubes,
green and black going to 1k big resistor and then to pin 4 of the power tubes,
and red seen to be the center.
Here are the impedance between the primary wires I got with the meter only(I did not hook it up on a power source):
brown / red = 150 ohms
blue / red = 2k ohms --- NOT GOOD!
green / red = 50 ohms
black / red = 50 ohms
According to those readings the OT is bad.
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According to those readings the OT is bad.
There is something not good indeed and that is my ability to read a analog meter LOL :laugh:
Verify the blue/red ohm readings, your reading appears to be an outlier when combined, I would have guessed from the other readings, it should be about 150 ohms and not 2K.
I did check it again, and the reading is about 172 ohms, does that sound right?
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I did check it again, and the reading is about 172 ohms, does that sound right?
Yes, much better. In a perfect OT each half of the primary winding would be exactly the same. But because of the way OTs are usually wound, one side will have a little more resistance than the other side. 150Ω and 172Ω are close enough, but 150Ω and 2KΩ raises a red flag.
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Do not forget to post any O/T labeled numbers. Look for a 6 or 7 digit number. With a little luck, those numbers will lead to the specs on the transformer, which will lead you to the question :
What power tubes do I use this this stated impedance?
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I did check it again, and the reading is about 172 ohms, does that sound right?
Yes, much better. In a perfect OT each half of the primary winding would be exactly the same. But because of the way OTs are usually wound, one side will have a little more resistance than the other side. 150Ω and 172Ω are close enough, but 150Ω and 2KΩ raises a red flag.
The OT can then be used in a new amp?
Do not forget to post any O/T labeled numbers. Look for a 6 or 7 digit number. With a little luck, those numbers will lead to the specs on the transformer, which will lead you to the question :
What power tubes do I use this this stated impedance?
There are no printings in the OT unfortunately, and the power tubes were missing. The choke have printing !
200mA 9Hy 140ohms
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Here is a thought,
Get a 6 to 9 volt AC 1 amp wall wart and connect the 6 to 9 volt AC output to the primary side of the OT, through a 10 ohm 10 watt resistor.
Now measure the voltage going into the primary with meter set to AC. Vin
Now measure the voltage coming out of the secondary with meter set to AC. Vout
Turns ratio = Vin / Vout
Impedance = Speaker Impedance X (Turns Ratio) X (Turns Ratio)
The math is off the top of my head, someone will soon correct me if its wrong.
Once you know the impedance it presents as a load you can choose a suitable set of tubes.
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From the listing of the assumed primary leads on the O/T, The power tubes could have been el34's KT's, 6V6's 5881, or maybe 6L6,
I agree with Franco, you need a schematic. There is a free download, JSCHEM available. Quite a few forum members are familar with the program. Maybe, we can match up parts with common applications.
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From the listing of the assumed primary leads on the O/T, The power tubes could have been el34's KT's, 6V6's 5881, or maybe 6L6...
I have the same feeling about it, and the OT is probably around 30-50watts output by the looks and size of it.
To me the first thing to be done is to reverse engeener the amp and draw the schematic
after that to convert it in a guitar amp will be simpler
as general roule
when you have under hand an amp that you want to convert
keep PI - Power Supply - Output Transformer as in the original amp
this will semplify a lot your life
Franco
Too late to map the circuit I was already half way disassembling the amp, and now it totally disassembled, thanks for the hint, I didn't want to convert the amp, the plan is to use the components to build a guitar amp, figuring out the OT will be possible to pick one that is known, with a layout and schematic, that way I think will be the best and easiest for me, because I'm not skilled enough in electronics to fiddle that much into an amp to convert it. I would have no clue about what to do, I'm just a noob!! :laugh: And this will be my second build !!
Oh by the way the amp was a real mess, cluttered soldering really nasty and sloppy work was done there, I wouldn't adventure in that "jungle", also there was some visible modifications, several switches(4), 3 of them I had no idea whatsoever what was the purpose.
I got some pics of the components:
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Lots of vintage quality parts to work with there.
Now that you've removed and cleaned them they are much nicer to work with. :icon_biggrin:
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Here is a thought,
Get a 6 to 9 volt AC 1 amp wall wart and connect the 6 to 9 volt AC output to the primary side of the OT, through a 10 ohm 10 watt resistor.
Now measure the voltage going into the primary with meter set to AC. Vin
Now measure the voltage coming out of the secondary with meter set to AC. Vout
Turns ratio = Vin / Vout
Impedance = Speaker Impedance X (Turns Ratio) X (Turns Ratio)
The math is off the top of my head, someone will soon correct me if its wrong.
Once you know the impedance it presents as a load you can choose a suitable set of tubes.
Figuring out at the moment how to hook the OT to find out the ratio, but I only have small DC power supplies with: 3, 5, 9 volts, does those have diodes ? (haven't open one yet) if the diodes are rectifying removing those will it give me AC output yes? Would that work to hook in the primary or secondary ?
Here a picture of the transformers.
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You have 6.3VAC CT (3.15-0-3.15) available on that big PT. Just connect that 3.15VAC to the secondary to do the voltage ratio measurements.
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I manage to get ±1vac source connecting some small transformers one after another :think1: , then I hooked it to the secondary of the OT, here is what I got as result, also follow a diagram of the OT.
prim blue/brown ±32vac }{ sec black/blue ±1vac
prim blue/brown ±25vac }{ sec black/brown ±1vac
prim blue/brown ±19vac }{ sec black/red ±1vac
does it make sense ?
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No, it doesn't make sense. In all three cases you put 1v across the black and blue secondary wires but got three very different voltage readings across the primary blue and brown wires.
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No, it doesn't make sense. In all three cases you put 1v across the black and blue secondary wires but got three very different voltage readings across the primary blue and brown wires.
Ooops I forgot to change the colors and words after copy paste, it is fixed now, also I have a diagram of the connections.
How about now ?
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Much better. :icon_biggrin:
If you put an 8Ω speaker across the BLK/BLU secondary wires you will reflect an 8192Ω load to the primary.
If you put an 8Ω speaker across the BLK/BRN secondary wires you will reflect a 5000Ω load to the primary.
If you put an 8Ω speaker across the BLK/RED secondary wires you will reflect a 2888Ω load to the primary.
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Much better. :icon_biggrin:
If you put an 8Ω speaker across the BLK/BLU secondary wires you will reflect an 8192Ω load to the primary.
If you put an 8Ω speaker across the BLK/BRN secondary wires you will reflect a 5000Ω load to the primary.
If you put an 8Ω speaker across the BLK/RED secondary wires you will reflect a 2888Ω load to the primary.
Which tubes can be used with those values ?
So with this numbers the OT seen to be working ?
I'm guessing the different wires in the secondary could be for 4Ω , 8Ω and 16Ω ? Is that right? Is there a way to find out ?
What amp can be build with this OT ?
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It seems to me the diagram is mislabeled. :dontknow:
I would expect the Turns Ratio numbers to go in order.
I don't see how the 19 TR could come in between 25 and 32.
Other than that, that OT should make a nice guitar amp. :icon_biggrin:
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It seems to me the diagram is mislabeled. :dontknow:
I would expect the Turns Ratio numbers to go in order.
I don't see how the 19 TR could come in between 25 and 32.
Other than that, that OT should make a nice guitar amp. :icon_biggrin:
Well I have no clue what the order would be... :laugh:
What amp can be build with the OT ?
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What amp can be build with the OT ?
Look at reply#18, then look at tube charts for your favorite ones, match up the primary values with the plate to plate data from the charts, then look up schematics that use them;
example, black-blue gives you 8kish, 6v6s and el84s like that, what amps use them....
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What amp can be build with the OT ?
Look at reply#18, then look at tube charts for your favorite ones, match up the primary values with the plate to plate data from the charts, then look up schematics that use them;
example, black-blue gives you 8kish, 6v6s and el84s like that, what amps use them....
Hey thanks shooter ! I was looking at that and trying to figure out, when I look at the tube charts I see different names like plate resistance and load resistance, are those the same thing ? Also in the same chart there are different values for the same tube, a bit confusing, I dunno which one to follow, I was wondering if is possible to use a pair of EL34, here 2 charts I was looking at:
http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf (http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf)
http://multcomercial.com.br/doc/valvulas/eh-el34eh.pdf (http://multcomercial.com.br/doc/valvulas/eh-el34eh.pdf)
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look at the 1st link, pg 4 Ra-a is 3.4k. which pair of wires gets you closest? OR, if you change the speaker from 8ohm to 4ohm, you can halve the primary impedance. You also need to look at *other stuff* on those charts, like your operating plate voltage, bias type, lots of cool things :laugh:
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look at the 1st link, pg 4 Ra-a is 3.4k. which pair of wires gets you closest? OR, if you change the speaker from 8ohm to 4ohm, you can halve the primary impedance. You also need to look at *other stuff* on those charts, like your operating plate voltage, bias type, lots of cool things :laugh:
Well the closest is black/red with 2888Ω.
Ok here is where things get confusing, I don't understand when the load is like 8Ω in each pair. there are 4 wires in the secondary of that OT, are the 3 pairs, each for different impedance, like 4Ω, 8Ω and 16Ω , or each pair can be used with any impedance ?
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To know what tubes, you must start with what B+ you can get from your PT and what is the likely power rating of the OT.
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each for different impedance, like 4Ω, 8Ω and 16Ω , or each pair can be used with any impedance ?
Yes :icon_biggrin:
In a known OT, say you have 8K primary and 3 secondary taps, 4 8 16, hook a 4ohm to the 4 ohm tap, it reflects back 8K. hook a 8ohm to the 8ohm tap, it reflects back 8K, BUT, hook a 4ohm to the 8ohm tap, it reflects back 4K. You'll have to hunt up the *why* math though
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To know what tubes, you must start with what B+ you can get from your PT and what is the likely power rating of the OT.
I have no idea what is the power rating of the OT, all I have is the numbers gathered by reading the wires.
The PT that came with this old amp says: primary 115v , 50cy
secondary 2x 350 volts , 200mA
5v , 4A - 6.3 , 5A , Ct
here is a pic:
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That OT doesn't appear to be original. The PT and choke both have cloth covered wires. The OT has plastic covered wires that make me think it comes from a later time period.
It's probably too late for this amp, but in the future try to gather as much info as you can about an amp BEFORE you start gutting it. Drawing a complete schematic complete with actual measured voltages would be ideal and yield invaluable info whether you intend to repair, convert, or just salvage iron. But even a partial schematic showing power supply and output tubes will give you a lot of good info. Surely more info than you have right now. At a minimum, try to determine what power tubes go with the amp. And pull the rectifier tube, then measure actual PT voltages.
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> gather as much info as you can about an amp BEFORE you start gutting it.
> even a partial schematic showing power supply and output tubes will give you a lot of good info.
+1
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That PT was made in Brazil, and on the front panel the word Linha means Line in Portugese. So looks like your iron at least is brazilian . As far as I know, the company Willkason is still going in Brazil.
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Thanks for the replies guys !!
That PT was made in Brazil, and on the front panel the word Linha means Line in Portugese. So looks like your iron at least is brazilian . As far as I know, the company Willkason is still going in Brazil.
Yes sir, you are correct, the amp was made down here in Brazil, but unfortunately I couldn't find any information about it, there is nothing online. Well I dunno if the Willkason is still going, but they make very good transformers, or at least they have the fame.
That OT doesn't appear to be original. The PT and choke both have cloth covered wires. The OT has plastic covered wires that make me think it comes from a later time period.
Yes that is what it looks like, they are indeed different.
Ok just want to remind you guys I can build this stuff if I have the schematic and specially a layout but, I dunno much about how it works!! :laugh:
Been having hard times trying to figure out the output impedances :BangHead:
It's probably too late for this amp, but in the future try to gather as much info as you can about an amp BEFORE you start gutting it. Drawing a complete schematic complete with actual measured voltages would be ideal and yield invaluable info whether you intend to repair, convert, or just salvage iron. But even a partial schematic showing power supply and output tubes will give you a lot of good info. Surely more info than you have right now. At a minimum, try to determine what power tubes go with the amp. And pull the rectifier tube, then measure actual PT voltages.
The amp didn't had rectifier tube or power tubes they were missing, there are no information what so ever on internet about this thing, I've look everywhere, no schematic, no manual, nothing, not even a mention anywhere about it, the amp was modified no doubt, already have mentioned all this before, I don't want to convert it or repair it, I just want to use the parts for a new amp, so it is a salvage operation. It is disassembled already, the OT is working what is good news, someone sujested a Plexi 50, and I do have the impression the power tubes on this amp were el34s, after looking at similar amps of that time many had el34s, so all left is on what known amp can the OT be used ? Would it work on a Plexi 50 with el34s ?
Thanks in advance !
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Would it work on a Plexi 50 with el34s ?
Probably. Give it a try. Let us know how it turns out.
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Would it work on a Plexi 50 with el34s ?
go back to your tube chart for el34, find filament current (X2), figure out how many 12XX7's you'll be using, get the fil current for 1 then multiply by tubes you'll use. Now you know how much PT iron you need to get the tubes warm, next settle on a happy plate voltage for the 34s. Now you can do some *bench testing* stuff with your unknown PT to see if it's up to the task.
EDIT: I just seen this from earlier;
The choke have printing !200mA 9Hy 140ohms
my guess is the manufacturer wouldn't use a 200mA choke in a 50mA circuit, and I'm pretty confident you will come in under 200mA with 2 34's
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Would it work on a Plexi 50 with el34s ?
Probably. Give it a try. Let us know how it turns out.
Ok cool, I still don't know which pairs of wires on the secondary of the OT are for 4Ω, 8Ω and 16Ω, how do I find that out ? :dontknow:
Would it work on a Plexi 50 with el34s ?
go back to your tube chart for el34, find filament current (X2), figure out how many 12XX7's you'll be using, get the fil current for 1 then multiply by tubes you'll use. Now you know how much PT iron you need to get the tubes warm, next settle on a happy plate voltage for the 34s.
The PT was running 4 preamp tubes, ecc83, ef86, 6sn7, 6sl7 and 2 power tubes.
Hmmm I can't find filament current there, but I've found Anode current, Grid No.2 current and Cathode current, which one of those refer to filament current?
Now you can do some *bench testing* stuff with your unknown PT to see if it's up to the task.
Do you mean unknown OT instead ? The PT is known.
The PT that came with this old amp says: primary 115v , 50cy
secondary 2x 350 volts , 200mA
5v , 4A - 6.3 , 5A , Ct
EDIT: I just seen this from earlier;
The choke have printing !200mA 9Hy 140ohms
my guess is the manufacturer wouldn't use a 200mA choke in a 50mA circuit, and I'm pretty confident you will come in under 200mA with 2 34's
So the choke isn't for too small stuff.
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It looks as if you choke was used on the plates as well. Considering 200ma. Cannot be certain tho since it is all apart.
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It looks as if you choke was used on the plates as well. Considering 200ma. Cannot be certain tho since it is all apart.
The choke was connected to filter caps look this pic:
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It looks as if you choke was used on the plates as well. Considering 200ma. Cannot be certain tho since it is all apart.
The choke was connected to filter caps look this pic:
They usually are. What I am asking is the choke BEFORE the first filter cap or did it connect the first cap to the second one. Meaning was it connected after the plates on the power tubes, but before the screens. If it were filtering the plates and you intend to use it in the same fashion you will have a voltage drop so instead of getting your approximate voltage unloaded using 1.41 multiplier for SS rectification, you multiplier becomes .88-.9.
Read up:
http://www.aikenamps.com/index.php/chokes-explained (http://www.aikenamps.com/index.php/chokes-explained)
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It looks as if you choke was used on the plates as well. Considering 200ma. Cannot be certain tho since it is all apart.
The choke was connected to filter caps look this pic:
They usually are. What I am asking is the choke BEFORE the first filter cap or did it connect the first cap to the second one. Meaning was it connected after the plates on the power tubes, but before the screens. If it were filtering the plates and you intend to use it in the same fashion you will have a voltage drop so instead of getting your approximate voltage unloaded using 1.41 multiplier for SS rectification, you multiplier becomes .88-.9.
Read up:
http://www.aikenamps.com/index.php/chokes-explained (http://www.aikenamps.com/index.php/chokes-explained)
Oh this seen to be a very good point, although I don't understand well how it works I can see the importance of matching the parts.
The wires of the choke were connected to a cap can 32+32µF/450-500v , each wire on the positive side of each cap in the can(the ground was in the other side of the chassis). At least that is what it looks like to me.
There is a pic of the cap cans at post #10.
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That's a nice pic of the choke wires! If you have some nice pics of the recto and output tube sockets post them as well. We may be able to get a good estimate of the tube types.
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From your question:
Ok cool, I still don't know which pairs of wires on the secondary of the OT are for 4Ω, 8Ω and 16Ω, how do I find that out ? :dontknow:
Sluckey showed the math on the impedance for 8 ohm speaker on each. The idea then becomes could do the same math for 4 or 16 ohms and see what those gave you. You'll likely find that the all come up to one consistently matching impendance when they're 'right' since there are three taps, probably 4,8,16, I'd guess the middle impedance of 5k would be the 8 ohm, and the other two would have a matching 5k impedance. Look at his math and compare. I'm probably going to get it backwards, but the 8ish k impedance one is likely 16 ohm and the 2ish one was the 4 ohm. Again, just repeat his math.
I may do it here in a second to confirm ;)
~Phil
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Ok so here's that math, lets see if this is right:
The windings ratio's per your check were:
32:1
25:1
19:1
I see the 8ohm was 5k at the 25:1 winding: 25^2 * 8
lets try 32:1 for 16 ohm
32^2 * 16
OOPS I had it backwards, that's 16,384
But if I do it for 4 ohm I get 4096, closer to that 5k impedance
Then that means if I do 19:1 with 16 ohm I get: 5776 also close to that 5k.
If you want to use the 4/8/16 windings, you'd want a tube output of around 5k. BUT you can just as well choose tubes that fit the ones I show above or any variation of the impedance on the secondary that you want, so long as the windings ratio and current capability of the transformer works.
~Phil
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Ok so here's that math, lets see if this is right:
The windings ratio's per your check were:
32:1
25:1
19:1
I see the 8ohm was 5k at the 25:1 winding: 25^2 * 8
lets try 32:1 for 16 ohm
32^2 * 16
OOPS I had it backwards, that's 16,384
But if I do it for 4 ohm I get 4096, closer to that 5k impedance
Then that means if I do 19:1 with 16 ohm I get: 5776 also close to that 5k.
If you want to use the 4/8/16 windings, you'd want a tube output of around 5k. BUT you can just as well choose tubes that fit the ones I show above or any variation of the impedance on the secondary that you want, so long as the windings ratio and current capability of the transformer works.
~Phil
I see !! That is what I was trying to figure out, yet I'm not sure how to pick the tube since some charts shows different values for the same tube, like in this chart: http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf (http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf)
So much to learn!!
Here what I did (note I got the ratio with a rudimentary apparatus giving about 1vac and the reading was done with an analog meter so I can't say for sure what is the exact number but very close to 19,25,32 :
32 * 32 = 1024 1024 * 4Ω = 4096Ω
25 * 25 = 625 625 * 4Ω = 2500Ω
19 * 19 = 361 361 * 4Ω = 1444Ω
32 * 32 = 1024 1024 * 8Ω = 8192Ω
25 * 25 = 625 625 * 8Ω = 5000Ω
19 * 19 = 361 361 * 8Ω = 2888Ω
32 * 32 = 1024 1024 * 16Ω = 16384Ω
25 * 25 = 625 625 * 16Ω = 10000Ω
19 * 19 = 361 361 * 16Ω = 5776Ω
That's a nice pic of the choke wires! If you have some nice pics of the recto and output tube sockets post them as well. We may be able to get a good estimate of the tube types.
Cool !!! Yeah here some pics !!
The white resistors are 50 ohms each on the PT_wires pic.
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I see !! That is what I was trying to figure out, yet I'm not sure how to pick the tube since some charts shows different values for the same tube, like in this chart: http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf (http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf)
So much to learn!!
Here what I did (note I got the ratio with a rudimentary apparatus giving about 1vac and the reading was done with an analog meter so I can't say for sure what is the exact number but very close to 19,25,32 :
32 * 32 = 1024 1024 * 4Ω = 4096Ω
25 * 25 = 625 625 * 4Ω = 2500Ω
19 * 19 = 361 361 * 4Ω = 1444Ω
32 * 32 = 1024 1024 * 8Ω = 8192Ω
25 * 25 = 625 625 * 8Ω = 5000Ω
19 * 19 = 361 361 * 8Ω = 2888Ω
32 * 32 = 1024 1024 * 16Ω = 16384Ω
25 * 25 = 625 625 * 16Ω = 10000Ω
19 * 19 = 361 361 * 16Ω = 5776Ω
Yeah basically now you can try and match anything that fits any of those. Then you just use the specific tap that matches that impedance on either side that you want. (i.e. if you like the 16k impedance you'll need to use a 16 ohm speaker and the 32:1 winding). If you want switchability between 4/8/16, you need to match up them all to be approximately that 5k level, and then choose output tubes that do push around 5k.
~Phil
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Yeah basically now you can try and match anything that fits any of those. Then you just use the specific tap that matches that impedance on either side that you want. (i.e. if you like the 16k impedance you'll need to use a 16 ohm speaker and the 32:1 winding). If you want switchability between 4/8/16, you need to match up them all to be approximately that 5k level, and then choose output tubes that do push around 5k.
~Phil
Thanks man , It is much clear now what it is all about, I think I got this !! So then if the desired impedance is 8k then use 8ohm speaker in the 32:1 wiring ? And all those numbers is what the OT can handle yes?
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@Ed_Chambley
I did read that info on the link you posted, thanks for the link.
I was looking at the classic tone choke for Plexi 50 stile here is the specifications:
Calssic tone Plexi 50: 3Hy 250mA 112Ω
Now this is the choke I have(Willkason): 9Hy 200mA 140Ω
Is the choke too big or too small or too big ?
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It's just right. The one in your hand is worth 10 in the bush.
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Thanks Sluckey !! By the way I got the pics you asked in the post #42 !!
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I saw them.
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Thanks man , It is much clear now what it is all about, I think I got this !! So then if the desired impedance is 8k then use 8ohm speaker in the 32:1 wiring ? And all those numbers is what the OT can handle yes?
Yes, that's correct, but that also means you wouldn't want to use the other windings and you should just cover them and make a single output jack. Some minor variances are okay, because the output tubes mirror what the OT is reflecting to them within reason, in your sample case a 16 ohm speaker may work fine in the 25:1 winding because its 10k and that's 'close' to the 8200 you're seeing in the 32:1, but I may be mistaken that it is safe, I don't yet understand what is a tolerable variance there.
~Phil
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I saw them.
Are the pics good enough to figure out what the power tubes could be ?
Thanks man , It is much clear now what it is all about, I think I got this !! So then if the desired impedance is 8k then use 8ohm speaker in the 32:1 wiring ? And all those numbers is what the OT can handle yes?
Yes, that's correct, but that also means you wouldn't want to use the other windings and you should just cover them and make a single output jack. Some minor variances are okay, because the output tubes mirror what the OT is reflecting to them within reason, in your sample case a 16 ohm speaker may work fine in the 25:1 winding because its 10k and that's 'close' to the 8200 you're seeing in the 32:1, but I may be mistaken that it is safe, I don't yet understand what is a tolerable variance there.
~Phil
Ok so it is good thing to have a switch for the different outputs?
Another thing that bugs me is the tube charts, in some old tube charts for the el34 I see the plate resistance under class B push pull, few numbers, they are at the line Raa~: 2.4 , 4.0 , 2.8 , 3.8 (this is what I should look for yes?)
those numbers are from the data sheet page 3: http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf (http://tubedata.altanatubes.com.br/sheets/010/e/EL34.pdf)
same from this other one: http://tubedata.altanatubes.com.br/sheets/128/e/EL34.pdf (http://tubedata.altanatubes.com.br/sheets/128/e/EL34.pdf)
so those two give about the same numbers.
Now in this other chart there is a totally different number, electro-harmonix one says 15k and it says nominal, what that means ?
Look those two(less info on those new datasheets):
http://multcomercial.com.br/doc/valvulas/eh-el34eh.pdf (http://multcomercial.com.br/doc/valvulas/eh-el34eh.pdf)
http://www.drtube.com/datasheets/el34-jj2003.pdf (http://www.drtube.com/datasheets/el34-jj2003.pdf)
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You are getting too tangled-up to unsort tonight.
The PT will give something near 350V with vacuum rectifier, over 450V with Silicon rectifier.
At 200mA, this means 70 Watts or 100 Watts of raw DC.
Tube amp is not much over 50% efficient. The "clean" audio output can be 35W or 50W.
35W-50W is up in the EL34 and 6L6GC class. (Or 6550/KT88 for extra-sturdy.)
The relation of push-pull OT nominal load to DC available (V/A) is near 2:1.
So the vacuum rectifier case wants like 3.5K load, the SI rect case wants 5K load.
At 5K load either the EL34 or the 6L6GC will do fine. The 6L6GC may be marginal at 3.5K and 4K may be a happier load for it.
Sluckey told you what impedances are possible from your OT tests.
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You are getting too tangled-up to unsort tonight.
Sorry about that. And thanks for the reply !!
Well I'm trying to learn but some things aren't very clear yet in my mind. Sometimes some language barrier may step in the way too, I'm not English born speaker.
And there are lots of things I yet don't really understand, I'll get there eventually.
And that may be why I might not be making the right questions.
I really appreciate everyones help !!!
The PT will give something near 350V with vacuum rectifier, over 450V with Silicon rectifier.
At 200mA, this means 70 Watts or 100 Watts of raw DC.
Hmm I'm not sure what the raw DC term means :w2:
Ok I did this little math here:
tube rectifier: 350v * 1.2 = 420 (i know depending on tube type it will change)
silicon rectifier: 350 * 1.4 = 490
does exist different diodes that can give different ratio lets say 1.3 ?
350 * 1.3 = 455 ?
I know this is what is gonna feed the amp B+. (only recently I find why it is called B+(batteries))
Tube amp is not much over 50% efficient. The "clean" audio output can be 35W or 50W.
35W-50W is up in the EL34 and 6L6GC class. (Or 6550/KT88 for extra-sturdy.)
The relation of push-pull OT nominal load to DC available (V/A) is near 2:1.
So the vacuum rectifier case wants like 3.5K load, the SI rect case wants 5K load.
At 5K load either the EL34 or the 6L6GC will do fine. The 6L6GC may be marginal at 3.5K and 4K may be a happier load for it.
What would be a happier load for EL34 ?
Sluckey told you what impedances are possible from your OT tests.
Yes that does help !!
I've just found this doc it may help others to understand transformers. Gotta read it.
https://nickzouein.files.wordpress.com/2012/03/transformer-calculations.pdf
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class B push pull
Most guitar stuff works in AB AB1, so whenever possible pick that on the tube charts. They also have columns with various plate, and screen(G2) conditions. so take the values you know, learned, find something close (+/-10%) and "run with it".
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> I find why it is called B+(battery)
No.
Early radios used *three* batteries.
Filaments
Plates
Grids
A lot of wires to hook up.
A+/- is filament (perhaps 1.5V at 0.5A)
B+/- is plate (135V at 20mA)
C+/- is grid bias (7.5V at zero mA)
Somehow "B" survived into the wall-power era but A and C names for supplies faded out.
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Regarding the choke,
I believe the O/T is wired down stream from the choke, as the plates and and one group of screens are fed from the transformer.
regarding reflected impedance, I would use the values for ultralinear tapping, to determine which tube was originally used.
If you are not going to use the O/T in U/L applications, then use the AB1 Raa values.
Regarding tap selection, Please do not put a 4 ohm speaker on you 16 ohm taps, I believe you might fry the O/T.
Also check out Hammond's 1650 transformer data specs. modified
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Regarding the choke,
I believe the O/T is wired down stream from the choke, as the plates and and one group of screens are fed from the transformer.
regarding reflected impedance, I would use the values for ultralinear tapping, to determine which tube was originally used.
Regarding tap selection, Please put a 4 ohm speaker on you 16 ohm taps, I believe you might fry the O/T.
Sorry,
OT is upstream from choke, usually. PT/Rectifier/OT B+/Choke
use the values for ultralinear tapping, to determine which tube was originally used.
How would that tell you what was used?
The KT88 data sheet specifically lists UL applications, others not so much.
You could use/not use the UL taps with most big bottles, no?
There really is no specific ohm tap, but there is a specific Z(Impedance) for each tap.
You can hook up whatever speaker load (4,8,16 ohms) x the taps Z that makes your output tubes happy at the voltage you are running them at, yes? :w2:
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All the tubes I listed have been used in U/L applications.
You are correct, getting info for u/l applications on a lot of tubes is difficult at the best.
Regarding 4 ohm on 16 ohm taps. The wiring gauge on 8 ohm and 16 ohm taps is typically finer (higher gauge number). than the 4ohm secondary windings. While you have higher turns for the 4 ohm windings, with the larger diameter wire, dc resistance is lower.
Look at the spec sheets for push pull transformers, the ratio of output voltage ratios are 1 for 4 ohm, 1.41 for 8 ohm and 2 for 16 ohm. PLEASE NOTE I MODIFIED MY PREVIOUS POST.
look at the ohm power calculator, P=V*V/R, leading to the conclusion that a 4 ohm speaker will demand 4 times the power than a 16 ohm speaker. and twice the power of an 8 ohm speaker. Hence the warning, do not hook up two ohm or 4 ohm speakers into a 16 ohm speaker jack.
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> I find why it is called B+(battery)
No.
Early radios used *three* batteries.
Filaments
Plates
Grids
A lot of wires to hook up.
A+/- is filament (perhaps 1.5V at 0.5A)
B+/- is plate (135V at 20mA)
C+/- is grid bias (7.5V at zero mA)
Somehow "B" survived into the wall-power era but A and C names for supplies faded out.
I did fix the post, Thanks!!
Hence the warning, do not hook up two ohm or 4 ohm speakers into a 16 ohm speaker jack.
Yes I'm aware of that, but it is always good to remind those important details, thanks!
Uncle Doug have a video about it, good info ! (speaker part start at 6:52) 1962 Fender 6G12-A Concert Amp Head (https://www.youtube.com/watch?feature=player_detailpage&v=cPg96DFp408#t=412)
Good thing you mentioned the UL taps, I've wondering after reading(file attached) some stuff about UL OT if it would work to use those taps in a Plexi 50?
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use those taps in a Plexi 50?
I've always used the UL taps when I have them, although I normally build SE not PP. They *generally* keep the grid voltage at some ratio below plate voltage, the one's I use are typically 40% tapped. You may still want to use a dropping R on G2 if you're running close to max on the tubes.
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use those taps in a Plexi 50?
I've always used the UL taps when I have them, although I normally build SE not PP. They *generally* keep the grid voltage at some ratio below plate voltage, the one's I use are typically 40% tapped. You may still want to use a dropping R on G2 if you're running close to max on the tubes.
In the original amp there were a big 1k resistor, maybe 10watts, between the tube and the OT. In the 1st post there is a pic where you can see it.
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If you're gonna build a Plexi just tape up the UL leads. If you're gonna build an old Sunn amp then use the UL leads. IOW, let the schematic you will build dictate when to use UL leads.
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If you're gonna build a Plexi just tape up the UL leads. If you're gonna build an old Sunn amp then use the UL leads. IOW, let the schematic you will build dictate when to use UL leads.
I see and I will follow you advise, thanks for the heads up. I would like to understand better why not. It is better not to use it due to the way the amp was designed, would it harm the amp or OT or make it sound bad ?
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I got cap cans with 32-32/450-500v from the Fidelius amp but the plexi says 50/500, the ones I have aren't close enough to the value or is it possible to use them ?
If not possible to use the 32-32/450-500v ones, would those small ones handle(really small size DIP 18*25 mm spec 47/500)?
http://pt.aliexpress.com/item/10pcs-lot-500V-47UF-DIP-Aluminum-Electrolytic-Capacitors-47UF-500V-Free-shipping/1860630005.html?spm=2114.02020208.3.36.0Kpq6Y&ws_ab_test=searchweb201556_10,searchweb201602_5_10017_405_404_507,searchweb201603_7&btsid=544a3864-0290-4e4c-bcd7-38f1f811a6eb (http://pt.aliexpress.com/item/10pcs-lot-500V-47UF-DIP-Aluminum-Electrolytic-Capacitors-47UF-500V-Free-shipping/1860630005.html?spm=2114.02020208.3.36.0Kpq6Y&ws_ab_test=searchweb201556_10,searchweb201602_5_10017_405_404_507,searchweb201603_7&btsid=544a3864-0290-4e4c-bcd7-38f1f811a6eb)