Hello rmyauck,
Speaking of the learning is fun that is the story of my life.
Lucy you have some splaining (Ricky to Lucy you know) to do. All the musty old books I have read circle the 43% tap point as the optimum UL tap point in the range between all in pentode and all out triode connected. Where did the 25% come from, that is out there from the old school way of doing things? I am asking because of interest. Is 25% UL tap something special to the 6V6?
All just for fun!
Speaking of the learning is fun that is the story of my life.
Lucy you have some splaining (Ricky to Lucy you know) to do. All the musty old books I have read circle the 43% tap point as the optimum UL tap point in the range between all in pentode and all out triode connected. Where did the 25% come from, that is out there from the old school way of doing things? I am asking because of interest. Is 25% UL tap something special to the 6V6?
All just for fun!
I thought the idea was to re-create the sound of your old Philco radio...
BTW, you should post some pics of the insides of your radio after your re-cap job.
'Blindly following a schematic' is not as easy as you may think; you'll need to make a few changes to that schematic, probably.
What about volume control? Input selector? Do you want tone controls?
"Where did the 25% come from, that is out there from the old school way of doing things? I am asking because of interest. Is 25% UL tap something special to the 6V6? "
I first read about it on the diytube form from Dave Gillespie. He gets it from the original Dynaco engineers thinking. 25% also applies to the EL84/6BQ5 types too. There was a discussion on this form earlier on in the year. It is mentioned in another place too with the different % for bigger tubes. He also mentions other OPT with a higher 10K input, will work fine for Cathode Bias if they are the standard 40-50% UL.
Here is one discussion in diytube.
diytube.com :: View topic - ST-35 with Tango Output Transformers
I just thought I would mention the transformers, so you got something good to work with, and possibly end up experimenting with different designs, as there are many out there. You can't blame the transformers if a circuit doesn't sound good to you.
I first read about it on the diytube form from Dave Gillespie. He gets it from the original Dynaco engineers thinking. 25% also applies to the EL84/6BQ5 types too. There was a discussion on this form earlier on in the year. It is mentioned in another place too with the different % for bigger tubes. He also mentions other OPT with a higher 10K input, will work fine for Cathode Bias if they are the standard 40-50% UL.
Here is one discussion in diytube.
diytube.com :: View topic - ST-35 with Tango Output Transformers
I just thought I would mention the transformers, so you got something good to work with, and possibly end up experimenting with different designs, as there are many out there. You can't blame the transformers if a circuit doesn't sound good to you.
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I have read somewhere that the EL84 likes the 25ish% tap, but that post on that forum thread was hinting that 6V6 would go with the 40ish% tap. (I somehow tought EL84 and 6V6 were similar tubes..?)
(for what its worth - I am far from a UL expert)
John, I was hoping to put volume control & tone control at the entry level of the amp; unless it is not a good idea?
Input selection I was hoping to have in a separate entity.
BTW replicating my old philco radio will not be made by following other schematics blindly either. Are you suggesting I follow the schematics of my old radio? I could look into that, I have its service manual and its schematics are available online.
http://www.nostalgiaair.org/PagesByModel/606/M0013606.pdf
look at page 82.
problem is: B+ pass trough the speaker's extra coil.
Although I realize... aren't the 6V6 connected in triode mode?
Here's my radio chassis how it currently looks like; with the power supply and amplifier recapped, I will attack the radio receiving stage soon.
It can currently receive AM and the phono input works like a charm, but FM is completely missing.
(for what its worth - I am far from a UL expert)
John, I was hoping to put volume control & tone control at the entry level of the amp; unless it is not a good idea?
Input selection I was hoping to have in a separate entity.
BTW replicating my old philco radio will not be made by following other schematics blindly either. Are you suggesting I follow the schematics of my old radio? I could look into that, I have its service manual and its schematics are available online.
http://www.nostalgiaair.org/PagesByModel/606/M0013606.pdf
look at page 82.
problem is: B+ pass trough the speaker's extra coil.
Although I realize... aren't the 6V6 connected in triode mode?
Here's my radio chassis how it currently looks like; with the power supply and amplifier recapped, I will attack the radio receiving stage soon.
An externally hosted image should be here but it was not working when we last tested it.
It can currently receive AM and the phono input works like a charm, but FM is completely missing.
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Hello,
I knocked the dust off of a couple of web links. In the 1950’s “Ultra-Linear” was patented see here acro
http://www.pmillett.com/file_downloads/acrosound.pdf
If the tap was not at 43% it was not UL. Prior the 43% the ACROSOUND guys wrote an article The Tube CAD Journal, Electrostatic Headphones Amps -Part 2-
An Ultra-Linear Amplifier
David Hafler* and Herbert I Keroes*
On page 2 Fig 2 shows a break point on the curve between pentode and 100% triode connection at ~20%. The 1955 patent gave ownership of “Ultra-Linear” and the 43% tap to ACROSOUND as optimum even for the 6V6. Nothing special about the 6L6 family or 6V6.
Now that the patents have run out we can tap where we like and call it UL if we like without paying ACRSOUND a dime in tribute.
I suppose we can run in pentode or triode modes or anywhere in between for that matter.
DT
All just for fun!
I knocked the dust off of a couple of web links. In the 1950’s “Ultra-Linear” was patented see here acro
http://www.pmillett.com/file_downloads/acrosound.pdf
If the tap was not at 43% it was not UL. Prior the 43% the ACROSOUND guys wrote an article The Tube CAD Journal, Electrostatic Headphones Amps -Part 2-
An Ultra-Linear Amplifier
David Hafler* and Herbert I Keroes*
On page 2 Fig 2 shows a break point on the curve between pentode and 100% triode connection at ~20%. The 1955 patent gave ownership of “Ultra-Linear” and the 43% tap to ACROSOUND as optimum even for the 6V6. Nothing special about the 6L6 family or 6V6.
Now that the patents have run out we can tap where we like and call it UL if we like without paying ACRSOUND a dime in tribute.
I suppose we can run in pentode or triode modes or anywhere in between for that matter.
DT
All just for fun!
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Volume control right after the amp input jacks is done all the time; no problem. Adding a tone control is more difficult- some of them require an extra gain stage to be added, unless the circuit was originally designed for a tone control. I don't know much about tone controls except in guitar amps. Many audio 'purists' don't like tone controls, it seems.
Replacing the field coil is no problem. Just add a choke to the power supply- right in the position where the FCoil is shown on the schematic(L100?). Replicating the power amp section of your Philco (x2 for stereo) would be a good learning experience, and you could certainly do that, I think. And the Philco has a tone control- if you like how it sounds just duplicate it as well.
In your Philco? No, they are pentode-connected. The screens get their own voltage from the power supply. You won't see 'triode-strapped' power tubes in much commercial gear because it drops the output power too much. The exception would be newer smaller guitar amps where the triode connection can be switched in for lower volume (and slightly different sound).
Good work in there- it can be pretty cramped in older gear, and tough to work without melting something. Don't forget they were assembled 'from the bottom up'....easier to build than to fix!
All the tubes have been checked or replaced with known good tubes?
I always keep hoping problems in my projects can be cured by new tubes - seldom works that way.
I must admit I still hope the "9th tube" on my Philco (the one that is used only for FM) is the culprit. The one I have lights up, but I have no way of testing it and didn't get a replacement yet.
You are right, those radio can be cramped to work in. Particularly the RF section of that model, which uses a smaller sub-chassis. There are capacitors under the shafts and things like that. Not fun to repair / recap!
The power and amp sections were easy in relation to the work ahead, and it was already something.
There is a lot more room after removing the old paper caps! (although I went overkill and got larger 1600V when "small" 600 was enough)
I think you're right, John. Replicating the amplifier stage of my old radio would be a better project to take on than redoing one of the many PP 6V6 projects out there. At least for me and what I am trying to get.
How would I alter the schematics to make it stereo? I guess the main changes would be the power section (bigger) and the chokes for the field coils?
How can I select a "similar" output transformer to the one in these schematics?
(or should I start hunting for vintage ones?)
Also... Is there any software for tubes schematics that I could use to recreate the amp and power sections of the Philco, where I could strip out what I don't need and alter for stereo...?
You are right, those radio can be cramped to work in. Particularly the RF section of that model, which uses a smaller sub-chassis. There are capacitors under the shafts and things like that. Not fun to repair / recap!
The power and amp sections were easy in relation to the work ahead, and it was already something.
There is a lot more room after removing the old paper caps! (although I went overkill and got larger 1600V when "small" 600 was enough)
I think you're right, John. Replicating the amplifier stage of my old radio would be a better project to take on than redoing one of the many PP 6V6 projects out there. At least for me and what I am trying to get.
How would I alter the schematics to make it stereo? I guess the main changes would be the power section (bigger) and the chokes for the field coils?
How can I select a "similar" output transformer to the one in these schematics?
(or should I start hunting for vintage ones?)
Also... Is there any software for tubes schematics that I could use to recreate the amp and power sections of the Philco, where I could strip out what I don't need and alter for stereo...?
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To convert to stereo you'd have to duplicate everything Well, except the power supply, there you could get away with only doubling the size of every component. In short it is the not practical.
Also... Is there any software for tubes schematics that I could use to recreate the amp and power sections of the Philco, where I could strip out what I don't need and alter for stereo...?[/QUOTE]
Are you looking from drawing software? Start with graph paper and pencil. But there are any number of drawing packages. What OS are you using? What's your budget.
Or are you looking for design or simulation software? If so most all of them are based on "Spice". Most have "spice" in their name. Some of these interface to schematic drawing software so that you can enter the design only once.
THat said, it's hard to beat a pencil.
Wouldn't I have to redesign the power supply stage?
we already stated that the 5Y3 wouldn't supply ennough for 4 x 6V6 tubes...
if we change the tubes, and the transformer (for more current)... then the whole power supply section isn't good anymore?
For software, I don't really want to do simulation, just have something to post for people here to correct me when I am wrong (here, I am assuming I'll do something wrong or maybe even stupid in the schematics...)
we already stated that the 5Y3 wouldn't supply ennough for 4 x 6V6 tubes...
if we change the tubes, and the transformer (for more current)... then the whole power supply section isn't good anymore?
For software, I don't really want to do simulation, just have something to post for people here to correct me when I am wrong (here, I am assuming I'll do something wrong or maybe even stupid in the schematics...)
Yes, the entire power supply would need to be either resigned so as to double the current or you'd build another identical supply. This second idea is the best as you'd also be building an other second amplifier
Best to build a stereo amp if you want one and keep this one as it is.
Got a scanner of a digital camera? Draw a schematic on paper. Ink over it then shoot or scan it. Adjust the image to make it "web size". This is quick and easy.
If you are looking for higher quality drawing. "Eagle" is not bad.
Downloads | Get The Latest Version of EAGLE | CadSoft EAGLE |
You can use it for small projects for free.
Another one that can make even nicer drawings and is also free is "xcircuit".
XCircuit
But be warned, all of this type software has a longer learning curve than a pencil. It will take a few days of study.
So the idea is to have two amplifier in one chassis, instead of having a stereo amplifier...?
Wouldn't this mean the resulting amplifier will be more power hungry?
I already had the service manuals scanned. I didn't really feel like using 60+years old paper. Here's a cut down version of the sections 1 & 2 that interests us: power and amplification.
I'll likely make a first version soon where I remove the useless things, such as the phono power plug. Maybe I'll keep the input selection...
we'll see from there where we go.
Tricky question... this uses half of an 7X7 tube. The other half is used in the radio for RF. What do we do with the "extra half" that we don't need? Is there a way to simply "shut it off"?
Wouldn't this mean the resulting amplifier will be more power hungry?
I already had the service manuals scanned. I didn't really feel like using 60+years old paper. Here's a cut down version of the sections 1 & 2 that interests us: power and amplification.
I'll likely make a first version soon where I remove the useless things, such as the phono power plug. Maybe I'll keep the input selection...
we'll see from there where we go.
Tricky question... this uses half of an 7X7 tube. The other half is used in the radio for RF. What do we do with the "extra half" that we don't need? Is there a way to simply "shut it off"?
Tek-
We are talking about leaving your Philco in its restored state and building a new amplifier, but using the ideas from the Philco schematic, right?
The power supply just has to supply enough current at the right voltages to drive the tubes. (...basically...) So you will have to design a new power supply to drive the two channels of amplification (stereo). I'm not a simulation guy either (pSpice is too much to learn) but I really, really like Duncan Amps PSUD software for designing power supplies.
PSUD2
And, it is free.
If you just post a power supply schematic and ask for comments, you are really asking other people to do your work. They will go to the software and do the simulation (or not...).
We are talking about leaving your Philco in its restored state and building a new amplifier, but using the ideas from the Philco schematic, right?
The power supply just has to supply enough current at the right voltages to drive the tubes. (...basically...) So you will have to design a new power supply to drive the two channels of amplification (stereo). I'm not a simulation guy either (pSpice is too much to learn) but I really, really like Duncan Amps PSUD software for designing power supplies.
PSUD2
And, it is free.
If you just post a power supply schematic and ask for comments, you are really asking other people to do your work. They will go to the software and do the simulation (or not...).
Two amps in 2 chassis, or 2 amps one chassis (rarer) are usually called 'monoblock'. Each amp has its own power supply. This can sometimes be as cheap as one larger power supply, because there are a lot of cheaper power transformers that can drive a mono amp (guitar transformers).
or,
a stereo amplifier - one larger power supply + 2 amps on 1 chassis.
If you are using without a preamp, and adding a volume control, don't you want to use one volume control (stereo pot) for both channels? With monoblocks you would pretty well have to adjust 2 controls.
Not much difference, IMO.
You could just ignore it if building monoblocks.
If you are building a stereo amp, use the other half for the other channel.
I think I'd rather have one main volume control instead of having two independant units.
So, section 1 would be completely redone, and there would be two identical section 2s... with the difference that the 7x7 would be shared.
Thanks for the link on PSUD2! That will certainly come in handy if I am to make my own power supply.!!
Plus, it seems the software was last updated ... today.!
So, section 1 would be completely redone, and there would be two identical section 2s... with the difference that the 7x7 would be shared.
Thanks for the link on PSUD2! That will certainly come in handy if I am to make my own power supply.!!
Plus, it seems the software was last updated ... today.!
The field coil speaker of my old radio is apparently 3.5 ohm; if I am to reuse the schematics, but work with 8ohm speakers, do I simply have to match the output transformers primaries?
What if I cannot get exact values, is that a huge issue? The primary impedance of the output transformer is 9000; I saw 8000 and 10000. Let say I get 8000, what are the impacts?
What if I cannot get exact values, is that a huge issue? The primary impedance of the output transformer is 9000; I saw 8000 and 10000. Let say I get 8000, what are the impacts?
If you are trying to build a second channel for stereo then yes it matters. Stereo is about creating an illusion where the sound seems to come from sources that are in a line that connects the two speakers. To do that you do need two IDENTICAL channels. Otherwise you just have a two speaker system, not stereo. Grossly mis-matched channels simply don't "image" at all. And you'd be better off with mono.
Assuming you want stereo, if you were to buy two new output transformers and two new speakers and they were 8K ohms rather than 9K you be OK. But don't waste your money trying to build a right channel with different parts than your existing left channel. use IDENTICAL design and IDENTICAL parts for both the left and right. In stereo the speakers are the most critical part, both have to be designed the same.
Assuming you want stereo, if you were to buy two new output transformers and two new speakers and they were 8K ohms rather than 9K you be OK. But don't waste your money trying to build a right channel with different parts than your existing left channel. use IDENTICAL design and IDENTICAL parts for both the left and right. In stereo the speakers are the most critical part, both have to be designed the same.
Tek- I'm assuming you are building all new, just using the schematic from your old radio. Please confirm this!
For 6V6 PP, usually anything around 7-9k seems to work for me. So now you just need to decide on output transformer budget ($) and what secondary taps you need- only 8Ω, or 4,8,16... and start shopping...
John
I am looking of building from scratch, but following the radio's schematics as much as I can.
Both channels would have matched identical components.
I was wondering if there was any changes to be done to the schematics to accomodate a different value transformer. It connects directly to the 6V6 pair... so do I understand that the 6V6 are OK under a certain range of values and as long as we remain in there its good without having to alter anything else?
how will the resulting audio be impacted if I augment or reduce the primary value on the transformer?
There are 10k PP output transformers out there, would 10k still be good?
Both channels would have matched identical components.
I was wondering if there was any changes to be done to the schematics to accomodate a different value transformer. It connects directly to the 6V6 pair... so do I understand that the 6V6 are OK under a certain range of values and as long as we remain in there its good without having to alter anything else?
how will the resulting audio be impacted if I augment or reduce the primary value on the transformer?
There are 10k PP output transformers out there, would 10k still be good?
You want to be in the 'right neighbourhood' of values - not too far from the accepted values. The circuit will work with a range of primary impedances; getting the best performance is the trick. It also depends on your speakers impedance curves- as the speaker impedance changes with frequency, the impedance that the tubes 'see' also changes. The transformer is basically a ratio device that reflects the speaker impedance 'back' to the tubes.
People do 'tricks' like connecting 8 ohm speakers to the 4 ohm tap on the transformer to double the impedance that the tubes see, for example.
I don't know if you have a good 6V6 datasheet handy.
This is a good one. Check pg 2 "Push-Pull Class AB1..."
Start a new thread for that, I think...lots of opinions on that. Most of the time I read that increasing the impedance tightens up the sound (less? bass) and reduces the power a bit. I don't know much about this stuff.
That would probably work. Check your voltages and the 6V6 spec sheet, and get some more opinions.
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