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Offline Ed_Chambley

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OT and understanding
« on: June 22, 2012, 07:40:57 am »
I have been reading lots of info on OT lately.  A couple of things I do not understand.  One company will make a OT for 6V6 at 8000 ohms and another will make it at 7000 and another at 6600.  Also, wattage comes into play and I have read in some places where you can benefit in using an overrated OT wattage and get better bass response.  For instance if you had a 40 watt 8ohm/6000 and used it in a 5E3, would it be an improvement or like Classictone sells a 8 ohm/8000 @ 20 watts for a 5E3 which they claim to be a replica of the original, whereas Mercury makes it 20 watts at 6600 and another at 7000.

These variations do not make any sense to me.  Can some of you guys chime in on what the differences are and what outcome you get if using larger iron and higher wattage.  I'm thinking you will lose volume output if using a larger wattage OT. Like using a 100 watter in a 50 watt Marshall.

Offline Tyrannocaster

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Re: OT and understanding
« Reply #1 on: June 22, 2012, 08:46:12 am »
I'm thinking you will lose volume output if using a larger wattage OT. Like using a 100 watter in a 50 watt Marshall.

I agree with your questions about why there are so many different impedance variations listed - it gets confusing. But that last sentence is incorrect. It won't sound the same if you use a heftier OT (well, it won't if your original one is stressed like the one in an old Fender tweed Deluxe) but, other things being equal,  it will be louder, and (personally, and I speak as somebody who owns an old tweed Deluxe) I think it will sound better. EDIT: of course, if the original OT is heftier than necessary you may not notice any difference. But that's a matter of personal preference and I have done enough of this to know that I like most of my distortion to come from the tubes and not the OT, although that can be a nice addition. But when the main component of the distortion is a strangled OT I don't like the way it sounds; some people love that cheap vibe but I don't.

The two best sounding overdrive-type amps I own both have way over-speced PTs and OTs. That 18 Watter that I posted the clip of, for example, has an OT at least three times as large physically as the one in my '55 Deluxe - probably bigger. Don't get me wrong - the '55 sounds very good, but not as good when driven all the way as the other amps; I like it better with lighter levels of drive. And my other great sounding amp (which also used EL84s and has fantastic distortion IMO) uses a Hammond 1650F OT wired in ultralinear mode, which is usually reserved for clean hifi applications. But that amp has gorgeous distortion.

I guess it depends on where you like your dirt to come from, but simply talking about volume alone, the bigger OT will be louder unless for some reason it is much less efficient.
« Last Edit: June 22, 2012, 11:20:28 am by Tyrannocaster »

Offline HotBluePlates

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Re: OT and understanding
« Reply #2 on: June 22, 2012, 01:42:21 pm »
... One company will make a OT for 6V6 at 8000 ohms and another will make it at 7000 and another at 6600.  ...

That's because there's no one, right, impedance for a given set of tubes.

There is a single impedance for a given set of tubes, B+, class of operation and operating point which delivers maximum clean power output. However, that single impedance may be a fiddly value, and often gets rounded up/down. If you go above or below the ideal impedance value, you'll either get more distortion, less power output, or both.

Unless you're using triodes and/or copious feedback, the amp won't have very good damping of the speaker, and the reflected impedance to the tubes will be all over the map. So your carefully selected impedance may not be the actual impedance all the time.

... I have read in some places where you can benefit in using an overrated OT wattage and get better bass response. ...

Yes, if your original situation pushed 20w of audio through a 10w OT. Look sometimes at the puny OT used with push-pull 6V6's in some consumer audio gear. I've seen some almost as small as a reverb transformer. It will still work, but the bandwidth gets constricted (roll off of both highs and lows), and there will be increased distortion due to core saturation. Kinda like tube distortion (where you run into either cutoff or saturation), but the cause is that the small core gets overwhelmed by the magnetizing current of the output tubes and doesn't accurately relay the power input on the primary to the secondary. There's likely to be power loss as well as distortion.

Flip side of this is if you want a VERY clean amp. Most Hammond transformers are rated for full power down to 15-30Hz. To accomplish that, the core has to be bigger, costing more $$$. But your guitar only goes down to 80Hz; do you really need another 2 octaves of bass response that you don't use? I say that as someone with an amp with such a Hammond. The OT is bigger than the PT. This amp does cleans extremely well, but part of that is the JBL D130 I'm using. But I wouldn't expect to need such an overrated OT in a 5E3.
 
Then again, you might like the sound of a bigger OT. The only way to know for sure is to try it. See if you can find a used OT for cheap. It's all theory until you actually do it.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #3 on: June 22, 2012, 02:28:34 pm »
I have about 20 or so OT's.  None of them are small and vary extremely.  I have never experimented as I do not understand what will happen.  One of my JTM-45 I would be willing to experiment with and I also have a 50 watt plexi.  The 50 plexi Has a Heybour replica of a 50 watt drake.  Both are 3400 for EL-34's and I usually build amps according to what I have heard someone else playing.  I say hey I like that and just copy it.  I have 3 builds going on right now, but only 1 is priority.  The other 2 are experiments.

Here is the deal.  Someone gave me a 5e3 Cabinet built out of pine and laminated in curly maple and has inlays in it.  It is beautiful.  So I am going to build something to go in it.  I like tweed amps, but the 5e3 seems simple and I have never considered building one.  I have a 5f4, a Bassman and low power twin.  People rave about the Deluxe but I don't get it probably because I have never owned one.  I prefer clean and punchy amps.  The reason for the questions on the OT is most tweed deluxe's I have seen have a small OT.  I think this is what makes them what they are.  I am trying to decide to build a deluxe for the cab as it was made for one.  Other than Neal Young, who else uses and prefers the tweed deluxe.  Every time I hear one it is got that dirt sound going.  I don't even know if one will clean up.

I hate not putting a deluxe in this cabinet as it is not something you see every day.  This is the reason for my questions.  Lots of people swear by them, but they are usually blues and rock players.  I really don't see it sounding good playing Jerry Reed.  Am I of base here?  This thing is really a showpiece of a cabinet.  Were there any other Fender amps that used the deluxe style cabinet that is a cleaner amp?  Whatever I put in it, I want it to be what would be expected in this type of cabinet.

Offline sluckey

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Re: OT and understanding
« Reply #4 on: June 22, 2012, 02:44:16 pm »
Consider putting a single channel with reverb only (AB763) in that cab. If it's the standard size cab, a 17" chassis and long reverb tank will fit. The Deluxe AB763 will get that Fender clean and some grind too. Kinda like this...

http://home.comcast.net/~seluckey/amps/tdr/tdr.htm
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline HotBluePlates

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Re: OT and understanding
« Reply #5 on: June 22, 2012, 03:58:16 pm »
... I really don't see it sounding good playing Jerry Reed.  ...

If you really want to sound like Jerry Reed (except for his occasional electric playing), you get a Baldwin 801CP classical with the Prismatone pickup (or a Harmony H174, and Sam Kennedy's Prismatone II), flamenco strings with red trebles. Then you get someone to do a crazy "cutaway" on it that chops away everything at/below the 18th fret.

 :icon_biggrin:

5E3's can play cleanly at fairly low volume. They just don't have a feedback loop or a lossy tone circuit, and so break up pretty low on the volume knob.

Example below of a guy employing the Baldwin (and a device to cancel Jerry's part from the Me & Chet album) to capture the Jerry Reed sound. It greatly helps if you have the chops (I don't, yet).

Phil Hunt - "Limehouse Blues" Jerry Reed parts
« Last Edit: June 22, 2012, 04:30:23 pm by HotBluePlates »

Offline TIMBO

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Re: OT and understanding
« Reply #6 on: June 22, 2012, 05:05:08 pm »
Good topic Ed,And it has given me food for thought. I have read posts that have used different speaker taps (4 ohms as 8ohms, 8 ohms as 16 ohms, etc.)  to increase/decrease primary impedance of an OT. I have an OT that i bought by mistake a hammond 1750K, 50 watts,4k primary with only one 2 ohm secondary.(bassman relpacement)

So thinking i now got an OT that i cant use( Speaker cab only wired for 4 ohms).

Thanks to HBP it seems there is hope for this OT.
If there is no real set match for OTs and power tubes am i thinking that this is possible :-
4k@2ohms would this translate to 8k@ 4ohms??
I have read that for a pair 6L6gc the primary impedance can be between 4k and 10k. Is this right??
Sorry if i  :hijack1: your topic but i thought it may be related.Thanks

Offline Tyrannocaster

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Re: OT and understanding
« Reply #7 on: June 22, 2012, 05:08:50 pm »
Ed, here are a couple more ideas to kick around.

I don't have a 5E3 but I do have a real '55 5D3. It gets really dirty fast, BUT if you change the phase inverter tube it can get some very good clean tones. I found this out one day when I didn't have anything better to do and I tried a 12AU7 in the PI; wow! Talk about a great Rockabilly amp! But, like I said, totally different PI and I can't speak for the 5E3.

The other idea is that you might consider an 18 Watt Lite for that cabinet. Before you dismiss the idea, I have built several of these and while they are not gain monsters and they aren't good surf music amps either, they are loud and they are very spanky before they start to break up. With just four tubes (plus rectifier) you won't be cramped for space like you might with some other amps. I think cathode biased EL84s are awesome for sounds that AREN'T overdriven as well as crunch, an idea that goes against most current small amp building practice.

HBP, the differing specs for OTs make it really hard for somebody who isn't much of an expert (read: ME) to get this straight because as soon as you say that impedance x is right for this pair of tubes you'll come across something that doesn't use that value but also sounds great. Trainwreck amps, for instance, often depart from "standard" OT values. I think your comment about the strangled 6V6 amps out there is right on because I must have encountered most of them! And what an astonishing difference getting rid of the puny OT can make! Off the topic, but I have been thinking that the new Fender Excelsior is a prime candidate for such a transplant. It's cheap, it has a pretty good idea behind it, and it has a tiny OT that just looks like it's really going to constrict the sound - presumably that's okay for its intended audience, which is not the usual Fender player. Put a big OT in it and maybe an efficient Eminence 15 (102 dB/1 meter) instead of the cheap stock 15 and I think you'd have a pretty loud amp. But like I said, the Excelsior isn't about volume (IMO), it's about vibe. And of course, your new modified Excelsior would cost you about $150 more than a stock one.

Also, Ed - if you have 20 OTs, can I come live in your neighborhood?  :laugh:

Offline PRR

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Re: OT and understanding
« Reply #8 on: June 22, 2012, 07:19:53 pm »
> I'm thinking you will lose volume output if using a larger wattage OT.

Why?

My house main electric draws about 10,000 Watts. The pole-transformer is 35,000 watts rating. Would I get less power at my house if they gave me a smaller 10,000 watt pole transformer?

No. Say the 35KW loaded with 10KW has 1% loss. Probably a 10KW loaded with 10KW would have 3.5% loss. The larger transformer is good for a couple extra volts at the house.

The main problem with "oversize" is weight and cost.

You could get in trouble with over-over-over-size. If Hydro dropped a 1,000KW lump to feed my 10KW house, just sitting there connected it would draw some idle current and demand more water over the generator dam just to keep it live. Hammond's 280W iron is perhaps more than a 2-6V6 DeLuxe should face.

As for 6K6 7K 8K 10K..... very nearly the same.

Offline HotBluePlates

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Re: OT and understanding
« Reply #9 on: June 22, 2012, 08:23:22 pm »
... as soon as you say that impedance x is right for this pair of tubes you'll come across something that doesn't use that value but also sounds great. ...

Exactly my point.

An AB763 amp is mostly 12AX7, right? But as you know, you can plug in all 12AU7, with cathode and plate resistors that are not "ideal" for the 12AU7, and it still works. It just works different.

It is possible to go too low on the OT primary impedance, with too high a B+ and too hard a grid drive. You might redplate your output tubes, or try to drive them to current peaks the cathode can't manage.

So there's a place for calculation, and we generally attempt to design for most clean power. But mostly, we're trying to get something that functions, not build a world-beating amp. And most all of this has been done before, since at least the early 60's if not farther back. That's the reason for copying known-good plans. The other reason is not every conceivable OT primary impedance and PT secondary voltage are available.

While you can pay someone to build just about anything if your cash is unlimited, most often we look for something approximately right that been done before and available.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #10 on: June 22, 2012, 08:53:18 pm »
Consider putting a single channel with reverb only (AB763) in that cab. If it's the standard size cab, a 17" chassis and long reverb tank will fit. The Deluxe AB763 will get that Fender clean and some grind too. Kinda like this...

http://home.comcast.net/~seluckey/amps/tdr/tdr.htm

Nice, Nice, Nice.  Thats bout all I can say.  What a tight build.  Got me a thinkin.  It was funny reading what you wrote.  It seems like every amp I build ends up being 6L6's or EL-34's.  I will look into the 4 tube EL-84 as an AC-30 is built this way.  The problem is when you see the cab you immediately think Custom Deluxe.  My favorite amp of all is AB763 with reverb.  I do not have the building skill of you and it looks like everything is shoehorned in.   I have a Weber 12A150, 25 watt Alnico I was planning to use.  I do not think it will fit with the build you made.  Maybe if I remove the bell.
« Last Edit: June 22, 2012, 09:28:46 pm by Ed_Chambley »

Offline Ed_Chambley

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Re: OT and understanding
« Reply #11 on: June 22, 2012, 09:00:57 pm »
... I really don't see it sounding good playing Jerry Reed.  ...

If you really want to sound like Jerry Reed (except for his occasional electric playing), you get a Baldwin 801CP classical with the Prismatone pickup (or a Harmony H174, and Sam Kennedy's Prismatone II), flamenco strings with red trebles. Then you get someone to do a crazy "cutaway" on it that chops away everything at/below the 18th fret.

 :icon_biggrin:

5E3's can play cleanly at fairly low volume. They just don't have a feedback loop or a lossy tone circuit, and so break up pretty low on the volume knob.http://www.el34world.com/Forum/index.php?topic=14004.0

Example below of a guy employing the Baldwin (and a device to cancel Jerry's part from the Me & Chet album) to capture the Jerry Reed sound. It greatly helps if you have the chops (I don't, yet).

Phil Hunt - "Limehouse Blues" Jerry Reed parts
I've ben opn tunin catgut strangs fer while now.  I like all his playing.  The double stop lead in East Bound is unbelievable and how he bot those chords to work together is magic.  Matter fact I am coping some licks right now.  I am not embarrassed at all to say I don't have those chops, but I got enough of them to make some covers we do interesting.  He is one of the greats.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #12 on: June 22, 2012, 09:11:17 pm »
Good topic Ed,And it has given me food for thought. I have read posts that have used different speaker taps (4 ohms as 8ohms, 8 ohms as 16 ohms, etc.)  to increase/decrease primary impedance of an OT. I have an OT that i bought by mistake a hammond 1750K, 50 watts,4k primary with only one 2 ohm secondary.(bassman relpacement)

So thinking i now got an OT that i cant use( Speaker cab only wired for 4 ohms).

Thanks to HBP it seems there is hope for this OT.
If there is no real set match for OTs and power tubes am i thinking that this is possible :-
4k@2ohms would this translate to 8k@ 4ohms??
I have read that for a pair 6L6gc the primary impedance can be between 4k and 10k. Is this right??
Sorry if i  :hijack1: your topic but i thought it may be related.Thanks
It is related.  It is what I have been researching the most.  the reason why is I built that 18 watt with cathode bias EL-34 and it was too hard to get clean.  I replaced the OT with a Mercury 8ohm/5900 and added 6l6 and them made it to switch in and out half of v2.  Changed to .0022 bypass.  Now I have a sparkling tone and extreme dirt on call.  No master anymore.  Don't need it.  Stil got some more things to try, but I think I have stumbled upon an original thing here.  I have some KT-66 I am going to try as well.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #13 on: June 22, 2012, 09:30:09 pm »
> I'm thinking you will lose volume output if using a larger wattage OT.

Why?

My house main electric draws about 10,000 Watts. The pole-transformer is 35,000 watts rating. Would I get less power at my house if they gave me a smaller 10,000 watt pole transformer?

No. Say the 35KW loaded with 10KW has 1% loss. Probably a 10KW loaded with 10KW would have 3.5% loss. The larger transformer is good for a couple extra volts at the house.

The main problem with "oversize" is weight and cost.

You could get in trouble with over-over-over-size. If Hydro dropped a 1,000KW lump to feed my 10KW house, just sitting there connected it would draw some idle current and demand more water over the generator dam just to keep it live. Hammond's 280W iron is perhaps more than a 2-6V6 DeLuxe should face.

As for 6K6 7K 8K 10K..... very nearly the same.
Thanks for this info.  This makes perfect sense.

Offline sluckey

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Re: OT and understanding
« Reply #14 on: June 22, 2012, 11:27:30 pm »
Quote
and it looks like everything is shoehorned in.
That was the biggest challenge about this otherwise fairly simple amp.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Tyrannocaster

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Re: OT and understanding
« Reply #15 on: June 23, 2012, 05:40:59 am »

I built that 18 watt with cathode bias EL-34 and it was too hard to get clean.  I replaced the OT with a Mercury 8ohm/5900 and added 6l6 and them made it to switch in and out half of v2.  Changed to .0022 bypass.  Now I have a sparkling tone and extreme dirt on call. 

See, that's what I'm having trouble with. The 18 Watt Lite should be able to get decent clean tones until you crank it up; I've built too many of them not to know that. It does have a much more limited tone stack than the Blackface Fenders, though. I wonder what the deciding factor in your dirt was? Now, with an extra gain stage (like Doug's Stout has) I can see the clean tones getting dirty, but he has a relay switch to cut it out of the circuit. To me that seems like the best of all worlds.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #16 on: June 23, 2012, 07:57:49 am »
Ed, here are a couple more ideas to kick around.

I don't have a 5E3 but I do have a real '55 5D3. It gets really dirty fast, BUT if you change the phase inverter tube it can get some very good clean tones. I found this out one day when I didn't have anything better to do and I tried a 12AU7 in the PI; wow! Talk about a great Rockabilly amp! But, like I said, totally different PI and I can't speak for the 5E3.

The other idea is that you might consider an 18 Watt Lite for that cabinet. Before you dismiss the idea, I have built several of these and while they are not gain monsters and they aren't good surf music amps either, they are loud and they are very spanky before they start to break up. With just four tubes (plus rectifier) you won't be cramped for space like you might with some other amps. I think cathode biased EL84s are awesome for sounds that AREN'T overdriven as well as crunch, an idea that goes against most current small amp building practice.

HBP, the differing specs for OTs make it really hard for somebody who isn't much of an expert (read: ME) to get this straight because as soon as you say that impedance x is right for this pair of tubes you'll come across something that doesn't use that value but also sounds great. Trainwreck amps, for instance, often depart from "standard" OT values. I think your comment about the strangled 6V6 amps out there is right on because I must have encountered most of them! And what an astonishing difference getting rid of the puny OT can make! Off the topic, but I have been thinking that the new Fender Excelsior is a prime candidate for such a transplant. It's cheap, it has a pretty good idea behind it, and it has a tiny OT that just looks like it's really going to constrict the sound - presumably that's okay for its intended audience, which is not the usual Fender player. Put a big OT in it and maybe an efficient Eminence 15 (102 dB/1 meter) instead of the cheap stock 15 and I think you'd have a pretty loud amp. But like I said, the Excelsior isn't about volume (IMO), it's about vibe. And of course, your new modified Excelsior would cost you about $150 more than a stock one.

Also, Ed - if you have 20 OTs, can I come live in your neighborhood?  :laugh:
You are correct about the neighborhood.  I grew up in a place called Forest Park Georgia.  It was a working class suburb of Atlanta.  My best friends father owned a TV/Radio/Audio Sales and Service store. The largest in the county.  His 2 sons were not interested in the repair portion of the store at all, but I was there in the repair shop learning to repair TV's which is no longer needed.  When he passed away about 10 years ago, he willed to me all his parts, tubes etc.  I have some really cool old TV's BTW.  Anyway long story even longer, I have at least 20 OT's, maybe more than 30.  Most are still in the original boxes and some have names I have never heard of.  They are mainly for HiFi so I never considered using them for guitar amps.  I am now thanks to HBP's reply.

IMO the best sounding small amp on the market today is the Egnater Tweaker combo.  Not the way they come, but replace those Ruby 6v6 and sovtek preamp tubes and it really comes alive.  It is Chinese and is about the size of a tweed deluxe.  None of the tubes hand down, they are all horizontal and the top is vented.

I am really digging Slucky's proposel and am thinking about doing it with horizontal tubes.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #17 on: June 23, 2012, 08:00:06 am »
Consider putting a single channel with reverb only (AB763) in that cab. If it's the standard size cab, a 17" chassis and long reverb tank will fit. The Deluxe AB763 will get that Fender clean and some grind too. Kinda like this...

http://home.comcast.net/~seluckey/amps/tdr/tdr.htm

Steve, if you still have the Visio files would you mind sending them to me?  They may be too big to post, if so send them to echambley@yahoo.com.

Offline sluckey

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Re: OT and understanding
« Reply #18 on: June 23, 2012, 10:45:48 am »
just made it...
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline sluckey

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Re: OT and understanding
« Reply #19 on: June 23, 2012, 07:30:25 pm »
Quote
At the risk of being ugly
Not ugly, just annoying. I honestly don't know what your purpose is. But I'm your huckleberry.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Ed_Chambley

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Re: OT and understanding
« Reply #20 on: June 23, 2012, 08:02:33 pm »
just made it...

Thank you Steve!  It was funny reading exactly what I wrote.  It is truely a nice looking amp.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #21 on: June 23, 2012, 08:08:47 pm »
Quote
At the risk of being ugly
Not ugly, just annoying. I honestly don't know what your purpose is. But I'm your huckleberry.

What does "I'm your Huckleberry?"

Offline HotBluePlates

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Re: OT and understanding
« Reply #22 on: June 23, 2012, 08:26:01 pm »
... One would fry a lot of  0/T's, if you fed it 30 or 40 Hz, for an extended period of time at the rated wattage.  ...

How?

If the OT is rated for that power, but not that low a frequency, you simply won't get all the power at that frequency out to the speaker. Probably because the core isn't big enough, which would then saturate at less-than-full-power, for that frequency.

What does "I'm your Huckleberry?"

It means Steve has seen too many movies about Tombstone and Doc Holliday.  :icon_biggrin:

Offline Ed_Chambley

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Re: OT and understanding
« Reply #23 on: June 25, 2012, 04:10:26 pm »
... One would fry a lot of  0/T's, if you fed it 30 or 40 Hz, for an extended period of time at the rated wattage.  ...

How?

If the OT is rated for that power, but not that low a frequency, you simply won't get all the power at that frequency out to the speaker. Probably because the core isn't big enough, which would then saturate at less-than-full-power, for that frequency.

What does "I'm your Huckleberry?"

It means Steve has seen too many movies about Tombstone and Doc Holliday.  :icon_biggrin:
I know what you mean now.  Val Kilmer says it.  I do not see how it applies unless you are going to die.

Offline sluckey

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Re: OT and understanding
« Reply #24 on: June 25, 2012, 07:24:04 pm »
Quote
And yes Sluckey you as a moderator have the power of a Hucklebearer.
Actually, I don't. But the fact that you dug up the true meaning, just goes to show that what I always thought about you is true... You are very intelligent and have a better than average understanding of what we're trying to do here. I simply don't understand why you want to piss on the forum. And that's why I'm your hucklebearer!

I would really like to invite you to join in to some constructive dialog. I think you may have some valuable input. And I'll certainly stay out of the way, if that's what it takes.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline HotBluePlates

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Re: OT and understanding
« Reply #25 on: June 25, 2012, 07:51:50 pm »
And if you saturate the OT for an extended period of time, what happens?  Cooked OT?

Not unless you're also exceeding the voltage and/or current ratings of the transformer.

Imagine you have an 8 oz glass, and you have it under a running faucet. There's a fair-sized hole near the bottom where water can run out.

Let's say you're filling the glass faster than the water can run out the bottom. Eventually, the glass will fill up and overflow. But the glass will stay intact unless you're filling it with a 150psi firehose.

It's an imperfect analogy, but a transformer makes use of the fact that current in a wire sets up a magnetic field around the wire. If you wind that wire in a coil, you can concentrate the field. Placing another coil nearby allows coupling from coil A to coil B, which is aided even further by adding a magnetic core to the mix.

Now a core can handle but some much of this magnetizing force before it's max'd out. So you can pump more energy into coil A, but beyond a certain limit, the core won't help transmit any more of that energy into coil B. The water running out the bottom hole can come out but so fast...

Maybe a better analogy is a 12AX7 gain stage. You can see by plotting a load line that it only takes maybe 4-5v peak to peak to run the full extent of a given load line. If you apply a 40v peak to peak signal, you won't get any more output at the plate, you just get closer to a square wave as the tube alternately saturates and cuts off. You'd think you might damaage something, but if the supply voltage isn't over 300v (doesn't exceed plate voltage rating), and the plate load resistor is 100k, you won't redplate the tube. No amount of input signal can cause it to draw more than 300v/100k = 3mA, 300v * 3mA = 0.9w. You simply get a more and more distorted output.

Similarly, unless there is some condition in place to allow your output stage to exceed the transformer's voltage and/or current ratings, applying too much power simply saturates the core and distorts the output to the speaker. Core saturation also results in a drop of primary inductance, so the bass doesn't extend as low as before, and is why O'Connor and others simply note you get "more distortion and less bandwidth."

And yes Sluckey you as a moderator have the power of a Hucklebearer.

The real question is, "where the hell is 'yonder' and why is everything over it?"  :icon_biggrin:
« Last Edit: June 26, 2012, 11:44:10 am by HotBluePlates »

Offline Tyrannocaster

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Re: OT and understanding
« Reply #26 on: June 26, 2012, 07:46:28 am »
I don't think he was trying to piss on the forum. I think English is not his native language, that's all.

Offline sluckey

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Re: OT and understanding
« Reply #27 on: June 26, 2012, 10:55:28 am »
Oh, I'm certain English is not a problem. Maybe I should be more sensitive.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline jjasilli

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Re: OT and understanding
« Reply #28 on: June 26, 2012, 11:02:26 am »

Offline Ed_Chambley

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Re: OT and understanding
« Reply #29 on: June 26, 2012, 03:53:19 pm »
I was just trying to get a better understanding of OT's.  Didn't mean to start a pissin contest.  Sensitivity is a flaw in character and takes some people time to outgrow it.  Being sensitive means you are injured by external sources, like having a sensitive tooth.  Compassion is having understanding of others.  Like walking in another mans shoes.

Give me a straight shooter any day.  I cannot learn anything from someone who is so willly nilly they are afraid of hurting my little feelings.  People who genuinely care tell you what they think as this means they care more about you than your feelings.

Maybe a thread about how amp discussions can hurt someones feelings. 

Well I did get some information so thanks.

Offline Ritchie200

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Re: OT and understanding
« Reply #30 on: June 26, 2012, 06:18:54 pm »
Well if that's the way you feel about it, this whole thread is stupid!



Oh sorry, I thought this was Tubenit's thread! - Ed, I hope I didn't hurt your feelings! :icon_biggrin:

I do have something (hopefully constructive) to add/ask....  I think the original question got sidetracked a little (at least for me).  PRR's example of the 6K6 mentioned that 7K, 8K, 10K are nearly the same.  So, my question is: Are there hard set rules of the sonic outcomes associated with these impedance's?  In other words, if we go up, what happens?  Does it roll off certain freqs?  Become compressed?  More distorted?  And vice versa -what happens when we go down?  At what % away from "ideal" does it drop off in performance?  At what point will we be beating the crap out of the OP tubes to detriment?

Hey, I'm just trying to be more touch sensitive!
Jim

My religion? I'm a Cathode Follower!
Can we have everything louder than everything else?

Offline Ed_Chambley

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Re: OT and understanding
« Reply #31 on: June 26, 2012, 06:43:10 pm »
Well if that's the way you feel about it, this whole thread is stupid!



Oh sorry, I thought this was Tubenit's thread! - Ed, I hope I didn't hurt your feelings! :icon_biggrin:

I do have something (hopefully constructive) to add/ask....  I think the original question got sidetracked a little (at least for me).  PRR's example of the 6K6 mentioned that 7K, 8K, 10K are nearly the same.  So, my question is: Are there hard set rules of the sonic outcomes associated with these impedance's?  In other words, if we go up, what happens?  Does it roll off certain freqs?  Become compressed?  More distorted?  And vice versa -what happens when we go down?  At what % away from "ideal" does it drop off in performance?  At what point will we be beating the crap out of the OP tubes to detriment?

Hey, I'm just trying to be more touch sensitive!
Jim
Now I'm crying.
This is what I was hoping for.  Great questions!  BTW, proper use of sensitive.

Offline HotBluePlates

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Re: OT and understanding
« Reply #32 on: June 26, 2012, 07:06:52 pm »
...  So, my question is: Are there hard set rules of the sonic outcomes associated with these impedance's?  In other words, if we go up, what happens?  ...  And vice versa -what happens when we go down?  At what % away from "ideal" does it drop off in performance?  ...

I already told you in my first reply!  :laugh:

There is a single impedance for a given set of tubes, B+, class of operation and operating point which delivers maximum clean power output. However, that single impedance may be a fiddly value, and often gets rounded up/down. If you go above or below the ideal impedance value, you'll either get more distortion, less power output, or both.

But don't take my word for it, look at the graph of the variation of load impedance with plate and screen voltage, bias and input signal held constant. The graph is from a fairly complete 6L6GC data sheet shows how plate current, screen current, power output and distortion changes when everything is held constant except load impedance.

Some data sheets have a graph like this. Some go further and show how 2nd harmonic and 3rd harmonic distortion change, as well as THD.

The graph is derived by setting tube operating conditions, drawing loadlines for each load impedance and analyzing the results for each load.

The graph assumed screen and plate voltage, bias and driving signal stayed constant. It shows there is an "optimum load" for most clean output power with the chosen operating point, and the trends that occur when you deviate from optimum.

Because most amps don't run the output tubes at 250v plate and screen, designers shoot for an optimum load impedance to produce maximum clean power (why else would you need to go to higher supply voltage, class AB, etc unless you wanted more power output?). They also recognize that the calculated 2497Ω ideal might not be practical, and based on observed trends understand that they will get a little less power output and a little more distortion when the optimum gets rounded up to the 4kΩ available part.

Offline Ed_Chambley

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Re: OT and understanding
« Reply #33 on: June 27, 2012, 12:28:56 pm »
I have been trying to understand these graphs.  I read where the term KNEE is used in reference to graphs.  What is the knee?  I started reading some amp books like Merlins and found out quickly I needed to step back so I got a book an Basic Electronics.  It is helping me a great deal.

I also wonder about these guys that write these amp books.  I have never heard of an amp built by Merlin Blencowe but he probably is an engineer who has worked on many projects for many companies.

I am getting some if it, slowly but surely.  I understand the graph is based on 250 v, but how does it help when you are at 417?  That's where the real knowledge lies I think.  Hell, I 50 years old and have a well established career and for some insane reason I have begun to be drawn to electronics.  So I am picking your brains.

Thanks!

Offline Willabe

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Re: OT and understanding
« Reply #34 on: June 27, 2012, 01:35:41 pm »
I read where the term KNEE is used in reference to graphs.  What is the knee?

The area where the line bends the most. Kinda looks like a bent knee.


                                Brad      :icon_biggrin:

Offline John

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Re: OT and understanding
« Reply #35 on: June 27, 2012, 02:48:58 pm »
Quote
I have never heard of an amp built by Merlin Blencowe but he probably is an engineer who has worked on many projects for many companies.

I forget where exactly I read it, but I believe Merlin is a serious hobbyist who wanted to publish a book with a lot of information all in one place, instead of scattered around the 'net. And yeah, I'd guess he's an engineer.  :icon_biggrin:
Tapping into the inner tube.

Offline TIMBO

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Re: OT and understanding
« Reply #36 on: June 27, 2012, 03:01:43 pm »
Hi guy's, I been reading this thread with the hope of resolving a little problem of my own ( to use a 4k/2ohm OT as a 8k/4ohm for a pair of 6L6s). I too have turn 50 and a carpenter that has trouble programming a VCR, i find that this HOBBY can get very technical in some areas and from what i can work out there are so many veriables and approximates are the key.

You guy's talk of ideal settings and thats great but to achieve that particular sound,tone and output power your amp would have to be the exact clone of a particular amp and this will never,ever,ever happen.

I don't have any tech training but i do have this forum and the knowledge here is priceless(and NOT always in a FREAK'N book).
I have found myself lost many times in the JARGON of electronics so i have had to at times rely on the"SUCK IT AND SEE" to get what i want and then it is only ME that might think it sounds any good.

And if you are like me and you have it sounding just right a little voice in your head tells you "this bit needs a little TWEAK and then it will be PERFECT. yeah right

Parts are expensive and explosions are costly but i think that if you are in the ballpark of the "APPROXIMATES" i think you will quickly work out if it is viable.
Keep up the good work as you all have input that is valuable to us untechicnal types. Thanks

Offline Tyrannocaster

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Re: OT and understanding
« Reply #37 on: June 27, 2012, 03:52:03 pm »
Hi guy's, I been reading this thread with the hope of resolving a little problem of my own ( to use a 4k/2ohm OT as a 8k/4ohm for a pair of 6L6s).

You shouldn't have any problems with doing that at all. That's actually a slightly different issue - we're talking about using a 4k/2ohm OT as an 8k/2ohm (using your example), or one of the other alterations you might try. I haven't done your example, but I did build an amp using a Twin OT with a pair of 6L6s (well, EL34s in the picture - I changed the bias) into an 8 ohm load. Since the Twin wants to use a 4 ohm load there was no problem and the amp sounds fine:

Offline sluckey

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Re: OT and understanding
« Reply #38 on: June 27, 2012, 08:15:01 pm »
Quote
I'll make a bet, say a Texas state quarter, that we could take the same circuit, say a 5E3, and 10 builders, boxes of similar quality parts, and it would still take some one with the experience of a Sluckey to fine tube the amp.   That's why we put knobs on the front of the amplifier.
You continue to reinforce my point. Still just a pissing contest to you.  :sad:

You might be surprised just how little experience a sluckey really has. I'm beginning to think your purpose is just an ankle biter. I'm gonna back off and see if you will prove differently. I hope so. Looking forward to your next build.

What a shame. You could probably contribute a lot to the forum and maybe even take something home too.



A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline HotBluePlates

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Re: OT and understanding
« Reply #39 on: June 27, 2012, 09:25:55 pm »
I have been trying to understand these graphs.  I read where the term KNEE is used in reference to graphs.  What is the knee?  

It's not in the graph I attached (at least not the knee you're talking about). The knee refers to the bend in the plate curves on the datasheet I linked, where a given gridline turns from horizontal to near-vertical as plate voltage drops.

I understand the graph is based on 250 v, but how does it help when you are at 417?

Grid bias gets more negative, grid driving voltage gets bigger. Absolute number for plate current, power output get bigger. Screen current might be a little bigger. Exact percentage of distortion may change slightly. But the general trends shown at 250v still hold at 417v.

What that means is you still see power output increase as load impedance gets bigger. Then there is a broad maximum where power output varies little over a fairly big change of load impedance. Keep going higher, and the power drops off again.

With graphs showing the percentage of 2nd and 3rd harmonic, you'll generally see 2nd increasing and 3rd decreasing (or vice versa) as load impedance changes. In hi-fi practice, a designer might choose a point where 2nd harmonic is very high, but 3rd harmonic is at a minimum. This point might not coincide with "maximum clean power"... but, the designer knows he'll use push-pull operation and 2nd harmonic will be cancelled at the output stage. The net result is maximum actual clean output power, even though the curves said that wasn't the case.

My point is, this stuff really can be simple and straightforward. You can be precise and complicated, or slightly less-precise and very easy. I used to make things too hard for myself. It took 10 years of reading and struggling to realize most of the answers were presented simply in the front of the RCA tube manual (and in more complex form in RDH3, 4).

The catch is when someone tells you the answer, it's like someone giving you the answers on your trigonometry homework. It's right, but you don't understand it enough to see how simple it could be. Once you really know it, you'll make things un-complicated, because you'll know the simple approach is not audibly different than the hard approach.
« Last Edit: June 28, 2012, 05:45:57 pm by HotBluePlates »

Offline Ed_Chambley

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Re: OT and understanding
« Reply #40 on: June 28, 2012, 04:54:27 pm »
I have been trying to understand these graphs.  I read where the term KNEE is used in reference to graphs.  What is the knee? 

It's not in the graph I attached (at least not the knee you're talking about). The knee refers to the bend in the plate curves on the datasheet I linked, where a given gridline turns from horizontal to near-vertical as plate voltage drops.

I understand the graph is based on 250 v, but how does it help when you are at 417?



Grid bias gets more negative, grid driving voltage gets bigger. Absolute number for plate current, power output get bigger. Screen current might be a little bigger. Exact percentage of distortion may change slightly. But then general trends shown at 250v still hold at 417v.

What that means is you still see power output increase as load impedance gets bigger. Then there is a broad maximum where power output varies little over a fairly big change of load impedance. Keep going higher, and the power drops off again.

With graphs showing the percentage of 2nd and 3rd harmonic, you'll generally see 2nd increasing and 3rd decreasing (or vice versa) as load impedance changes. In hi-fi practice, a designer might choose a point where 2nd harmonic is very high, but 3rd harmonic is at a minimum. This point might not coincide with "maximum clean power"... but, the designer knows he'll use push-pull operation and 2nd harmonic will be cancelled at the output stage. The net result is maximum actual clean output power, even though the curves said that wasn't the case.

My point is, this stuff really can be simple and straightforward. You can be precise and complicated, or slightly less-precise and very easy. I used to make things too hard for myself. It took 10 years of reading and struggling to realize most of the answers were presented simply in the front of the RCA tube manual (and in more complex form in RDH3, 4).

The catch is when someone tells you the answer, it's like someone giving you the answers on your trigonometry homework. It's right, but you don't understand it enough to see how simple it could be. Once you really know it, you'll make things un-complicated, because you'll know the simple approach is not audibly different than the hard approach.
The catch you refer to is what I am wanting to avoid.  When I built a replica of  Fargen Ole 800, it was easy.  I opened one up.  Ordered the exact parts and got Jeff at JD Designs to send me the white cabinet.  Didn't know what I was doing.  My first build.  Of course it came out great and the amp is envied by many I play with.

Things do not become in-complicated until you have that mental click.  I have been told "you think too much" and I respond maybe you think too little.  I get your drift tho.  I also understand your explanation of the 250-417 voltage.  Thank you for that.

I don't know where I am going with this, but I have always been able to fix amps because as a teenager I worked in a TV repair shop.  Remember tube TV's? But designing amps is very interesting.  It is the harmonics which tubes generate is where I am focused.  Of course I am having to learn to draw schematics (Slucky is insuring that and I am not complaining).  There is a lot to this and it can be very simple, but where is the fun in that?

In my experimenting I have learned some very cool things.  Most of my experiments are on the negative side, but those are valuable.  I am just not the part changer kind of person.

Since the beginning of this thread PRR's comments lead me to attempting some over-sized OT.  I put a 100 watt Heybour in a JTM-45 (modded to be very clean) and kept the original one in as well and made a footswitch for it.  I was hung up so much because I did not know.  To say there is not much difference would be the understatement of the year.  Mismatched, yes.  Thinking it would get louder and cleaner, boy I was wrong.  It went very brown.  I don't know why, but I will know soon.

Offline Ritchie200

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Re: OT and understanding
« Reply #41 on: July 01, 2012, 12:23:19 am »

I already told you in my first reply!  :laugh:


HotBluePlates, what the hell?!?!?!  You expect me to read EVERY post in this thread?!?!  Jeez...

My next question is: As the grid bias gets more negative, what happens to the grid driving voltage?  And what is a knee?

Yer pal,
Jim

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Can we have everything louder than everything else?

Offline Ritchie200

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Re: OT and understanding
« Reply #42 on: July 01, 2012, 09:43:50 pm »
Now you guys know I be kidding - right? :wink:

HBP, you are not returning my calls! :sad2:

Thanks for a great explanation!
Jim

My religion? I'm a Cathode Follower!
Can we have everything louder than everything else?

Offline Willabe

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Re: OT and understanding
« Reply #43 on: July 02, 2012, 12:29:02 am »
I keep tellin you Jim, your gonna get a Tele from Santa for Christmas.     :w2:


                         Brad      :l2:

Offline Ritchie200

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Re: OT and understanding
« Reply #44 on: July 02, 2012, 04:38:39 pm »
OH COME ON!!!!!  I'm not THAT bad....

Jim

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Can we have everything louder than everything else?

Offline Ed_Chambley

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Re: OT and understanding
« Reply #45 on: July 02, 2012, 08:10:37 pm »
I keep tellin you Jim, your gonna get a Tele from Santa for Christmas.     :w2:


                         Brad      :l2:
I would hope so, the tele is the best damn guitar ever.  Don't think so?  You Tube Danny Gatton.

Offline Willabe

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Re: OT and understanding
« Reply #46 on: July 02, 2012, 09:11:44 pm »
Uh-oh, now you did it.


                   Brad      :w2:

Offline Ed_Chambley

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Re: OT and understanding
« Reply #47 on: July 03, 2012, 11:26:35 am »
Uh-oh, now you did it.


                   Brad      :w2:
I would reply, but then I would Hi-Jack my own thread.

Offline Willabe

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Re: OT and understanding
« Reply #48 on: July 03, 2012, 12:11:40 pm »
I would reply, but then I would Hi-Jack my own thread.

 :hijack1:         :laugh:

Jim and Tubenit have a friendly disagreement about Tele's and Strats.


                Brad      :m8

Offline Ritchie200

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Re: OT and understanding
« Reply #49 on: July 03, 2012, 09:56:30 pm »
I would rather have the coal, it has better tone.

And who ever said it was "friendly"?

Jim :icon_biggrin:
 :m8
« Last Edit: July 03, 2012, 09:59:21 pm by Ritchie200 »

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Can we have everything louder than everything else?

 


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