Starting a D'Lite

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ChrisM
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Re: Starting a D'Lite

Post by ChrisM »

If you use 1/4W, which is fine...Just to be safe attach the cap to the plate and the resistor to the grid.
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Structo
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Re: Starting a D'Lite

Post by Structo »

Dreric,
There is another mistake on that layout you grabbed.

The Master Volume should be 1MA not 500KA.
Tom

Don't let that smoke out!
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dreric
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Re: Starting a D'Lite

Post by dreric »

Thanks Guys!!!!!

I'm going to respond to a few questions as well as ask a few more.

Bigmik: No gromets, those holes are actually beveled nicely and very smooth (hard to see in the photos). Seeing that there is no strain on the wires coming through I'm thinking it's ok.

Tom: You're right, I found the 22M very hard to source, got some nice 1 watt "powers" from mouser that are the size of tootsie rolls but ended up with the two watts that are there now, glad to here that they will work and nice to know that 1/2 watt is an option.

And yes, thanks to your due diligence on the board I was already aware of the MV pot being 1 meg.

I had a dialogue with RJ who supplied the chassis and transformers he said that when he first put this set together (it was for his personal use) he was thinking of using 2 6V6 or 2 KT-66 as power tube off the primaries. Seeing that KT-66 want 5000 for zOut/load resistance and I have a few pairs about..............hmmmmm?

All of this brings me face to face with my ignorance and I am hoping for some direction. Please correct me when my understanding fails:

The output transformers has a primary impedance that should be matched to the tubes "zOut"? zOut is that same as the older designation of "load resistance" AND it varies based on what class the tube is operating within. Example from the RCA manual, 6L6GC in class A wants a load resistance of 4200 ohms, in class AB1 3800 ohms.

I don't understand if this data is for a single tube or pairs quads etc. Does a single tube and or pair of 6L6 want to see 4200 for class A and 3800 for class AB1?

When it comes to output transformers how do you establish the values of the primary's???? I have three different output transformers on hand and when I take measurements across the primary leads I don't get resistance numbers that make sense to me. Do I need to supply the transformer an electrical load like a power transformer?? If you are supplying a load at what voltage (AC?) and won't that affect the measurement of the primary? Is there an established method?

Lastly, what is the impact of different speaker impedance on the primary. I don't understand how the assumption of speaker load is assumed by primaries of the output transformers.

Thanks in advance for pondering these questions, also if there is some reference book or resource that explians all this feel free to point it out.

Eric
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Structo
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Re: Starting a D'Lite

Post by Structo »

In the tube manuals when they give a output impedance and it says A/B or push/pull that is for two tubes.

Yes, you won't be able to measure the impedance by any normal means.
You can measure the DC resistance and that is what you got when you used your meter on it.

Impedance is a reactive property having to do with inductive reactance and frequency.

So when they say this OT has a primary impedance of such and such, it is for a particular frequency and reactive load.
It is not a static number as it moves all over the place with the signal applied.

What you will find out usually, is peoples recommendations for a certain use in an amp.
Say for a 2 x 6L6 amp you want a primary of 4200 or for 4 x 6L6 you want 2200. (those aren't etched into stone).

The best output transformer will maximise the output of the power tubes to their best.
Although sometimes people manipulate numbers for a chosen characteristic.

Many transformers will work but for them to be at their most efficient, the recommended numbers should be followed.
Tom

Don't let that smoke out!
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ChrisM
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Re: Starting a D'Lite

Post by ChrisM »

Structo wrote:In the tube manuals when they give a output impedance and it says A/B or push/pull that is for two tubes.

Yes, you won't be able to measure the impedance by any normal means.
You can measure the DC resistance and that is what you got when you used your meter on it.

Impedance is a reactive property having to do with inductive reactance and frequency.

So when they say this OT has a primary impedance of such and such, it is for a particular frequency and reactive load.
It is not a static number as it moves all over the place with the signal applied.

What you will find out usually, is peoples recommendations for a certain use in an amp.
Say for a 2 x 6L6 amp you want a primary of 4200 or for 4 x 6L6 you want 2200. (those aren't etched into stone).

The best output transformer will maximise the output of the power tubes to their best.
Although sometimes people manipulate numbers for a chosen characteristic.

Many transformers will work but for them to be at their most efficient, the recommended numbers should be followed.
Other way around. :wink:

Other than that, great explanation.
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Structo
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Re: Starting a D'Lite

Post by Structo »

How do you figure?
Two 6L6's in parallel with two 6L6's = 2K-3K
Tom

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ChrisM
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Re: Starting a D'Lite

Post by ChrisM »

Fack, read your post wrong, sorry.

Shouldn't be browsing here while trying to my calc work. Carry on... :oops:
vibratoking
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Re: Starting a D'Lite

Post by vibratoking »

A comment about impedance. Not to be a stickler, but for a more complete understanding.

You can modify Ohm's law in a general way by replacing the word resistance with the word impedance. Impedance is in fact 'generalized resistance'. Capacitors and inductors have reactance, while resistors have resistance. Impedance = resistance + reactance. If reactance = zero then impedance = resistance. So we can speak of impedance for purely resistive circuits or for those with reactance.

Capacitors and inductors have a reactance that is dependent on frequency. At any frequency the reactance can be expressed in Ohms and combined with any series or parallel resistive elements. This could go on... I hope this makes it more clear.
talbany
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Re: Starting a D'Lite

Post by talbany »

How I always thought of it is altering resistance ( resistors, pots, tubes, transformers, etc) in a circuit changes impedance.. Impedance being frequency dependant alters tone.. For instance the 2 resistors that feed the ratio/ drive pot 100k/ and 150k that feeds the OD level in a Non HRM/ D-Lite there primary purpose is for tone shaping...adding resistance raise impedance alters tone..The pots also effect impedance.. Resistance effects impedance...impedance effects frequency response..in that order..(in general raising resistance darkens tone for lack of a better word)
In the case of OPT primary impedance I would place the emphasis on maximum transfer of energy..

Tony
" The psychics on my bench is the same as Dumble'"
vibratoking
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Re: Starting a D'Lite

Post by vibratoking »

Talbany, your post is interesting to me because it starts to correlate tone with components. This is an area for which I have little experience.

I commented on impedance because I got the impression that it wasn't fundamentally understood after reading some of the previous posts. I hope it helps.

Impedance = resistance + reactance. So changing any component in the signal path changes the impedance and therfore the tone.
(in general raising resistance darkens tone for lack of a better word)
For me, the phrase that corresponds to darken is frequency content. I think of tone in two primary ways, frequency content and transient response. I'm not sure that raising resistance always darkens the tone or reduces the frequency content. It depends on the topology of the circuit - i.e. how the reactive components are placed in relation to any specific resistance.

This is an interesting subject, but I don't want to hijack the thread.
Maybe I should start another thread.
[/quote]
talbany
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Re: Starting a D'Lite

Post by talbany »

Yeah!! Another Topic!!
" The psychics on my bench is the same as Dumble'"
IcemanB52
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Output Xfmr

Post by IcemanB52 »

dreric wrote:Thanks Guys!!!!!

Lastly, what is the impact of different speaker impedance on the primary. I don't understand how the assumption of speaker load is assumed by primaries of the output transformers.

Eric
The role of the output transformer is to "transform" the speaker impedance to the impedance required by the power tubes. The manufacturer does this by means of the ratio of the primary to secondary turns of wire on the transformer. If you put several taps on the secondary side of the transformer, you can switch between different speaker impedances while keeping the primary impedance constant. Hope this helps. Richard
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dreric
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Re: Starting a D'Lite

Post by dreric »

Thanks to all for furthering my education. Please don't worry about derailing threads, I can always swing it back around.

The impedance / resistance stuff is starting to make some sense and I'm reading (or trying to) all the books I've collected over the years. Waiting for that critical mass of information to jell into "oh I got it"! it will happen.

I'd like to ask this question in a different way.

Let's say that you have what you know to be output transformers, but that's all you know. How would one go about figuring out how to use them? Yes, I know I can look up model number and laboriously search through schematics till I find how it was used. I want to know WHY they are used the way they are.

Eric
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ampdork
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Re: Starting a D'Lite

Post by ampdork »

"...& I'm all out of bubblegum"
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topbrent
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Re: Starting a D'Lite

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