Dynaco A-50 tweeter help needed?

[Guest matty g]

Hi John

If you haven't purchased a pair of tweeters for your beautiful A-50s yet I have a pair of Seas units from my A-25s that are in good working order. I won't be needing them and I'd rather sell them to someone associated with this forum than on that E-place. If you are interested, please e-mail me at mjgrover@peoplepc.com and we can work something out. You've gotta watch out when you buy drivers on Ebay - you never know where they've been!

Hope you get the bugs worked out of those beauties...they are going to sound as good as they look...AWESOME!

Matt

[jwjensen356]

Hi, this is my first post. And I am very happy being here.

I have a pair of A-50s that I bought in November and I love 'em. Here is my question and it is regarding the frequency range of the individual 10" drivers. I noted the separate discussion regarding the AR-94s (in a separate section of Classic Speakers). The comment was made "The lower bass unit is rolled off before the upper one, and in that sense, is made to reinforce the upper unit in the extreme bottom end". Have I noted the same thing with the A-50s?

The cross-over for the AR-94 shows that the two woofers are not directly in parallel but have additional L and C circuitry. But in the circuitry that I have found on the internet for the A-50s, the two woofer speakers are directly in parallel. However, I have noted a similar effect when putting my ear to the speaker cabinet for speaker 'A' and 'B' of the left and then to the right ('A' and 'B'). One seems to respond more to lower frequencies than to higher. Am I imagining things? Opinions please.

John

[dynaco_dan]

>Hi, this is my first post. And I am very happy being here.

>

>I have a pair of A-50s that I bought in November and I love

>'em. Here is my question and it is regarding the frequency

>range of the individual 10" drivers. I noted the

>separate discussion regarding the AR-94s (in a separate

>section of Classic Speakers). The comment was made "The

>lower bass unit is rolled off before the upper one, and in

>that sense, is made to reinforce the upper unit in the extreme

>bottom end". Have I noted the same thing with the

>A-50s?

>

>The cross-over for the AR-94 shows that the two woofers are

>not directly in parallel but have additional L and C

>circuitry.

But in the circuitry that I have found on the

>internet for the A-50s, the two woofer speakers are directly

>in parallel. However, I have noted a similar effect when

>putting my ear to the speaker cabinet for speaker 'A' and 'B'

>of the left and then to the right ('A' and 'B'). One seems to

>respond more to lower frequencies than to higher. Am I

>imagining things? Opinions please.

>

>John

Hi John;

I just noticed this un-answered question, sorry.

Both of the 2 - A-50 16 ohm woofers are in parallel and operate at the same frequencies.

Normaly you will not notice any difference between them in performance, even so there is a factory tolerance.

If there is a substantial sonic difference, then one or both are damaged, out of phase or mismatched.

I am assuming that the driver/cabinet fit is well sealed.

[dynaco_dan]

Hi again;

To add to our Dynaco knowledge, I have downloaded a copy of 3 Dynaco A-50 sheets.

I do not own the originals or take the photos.

Note photo 1 is a repeat of an earlier posting, see the A-50 tweeter location and internal partition location.

Photo 2 has a smaller inset drawing with the different tweeter location and partition board location as well.

Photo 3 just some more handy information, particularly each switch step is about 3 dB+/- at 10khz.

This data should also be the same for the 5 position A-25 and A-35 speaker systems.

They claim that normal is the switch position where most normal listeners listen.

I guess I'm not normal, using the maximum position myself.

Now I don't need to guess anymore on the switching changes in output.

The recommended minimum 18 guage wire for the speakers.

I do not know which internal partition location was the final version or which tweeter location was the final version.

That information may be forthcoming in the future.

[dynaco_dan]

Hi again;

Some more thoughts about the Dynaco 5 position crossover switch.

I am referring souly to the Dynaco A-35 crossover 5 position switch board here, the A-25 and A-50 should be identical though.

With the tweeter level set at maximum CW, there is but a single 8uf 25v AC/50v DC NP non-polarized electrolytic cap, and also a single 2.2 ohm 3 watt sandcast resistor and the wire which I will guess at maybe 24 guage if that large, in series with the tweeter.

Typically your regular house electrical wiring will be 14 guage and your 24 volt heating thermostat wire will be 19 guage, 24 guage is about 1/16" od, the insulation that is, or close to thread size copper wire, not very large.

Moving down the scale to soften the treble, the next 4 positions CCW adds 2.2 ohms at each stepped setting, or 8.8 plus the permanent first one, for a total of 11 ohms in series with the tweeter at the lowest setting.

Dynaco states on the previously listed information sheet that each step is equal to about 3dB @ 10khz.

I feel that if one wanted to be daring, they could bypass the first permanent 2.2 resistor and increase the brightest output by another 3dB.

This single permanent resistor may be the reason I have not seen but a very, very few burnt out tweeters, maybe?

This also may be an engineered preventitive step to lessen the chance of tweeter overload.

I don't think that a manufacturer would just thrown in a spare resistor for the fun of it, they may have had tweeter burnouts early on and modified later production with this extra resistor.

The increased level output may place it up in output, at least as far as the tweeter is concerned, up next to the A-25XL.

I would wait for others to comment about this idea before attempting it.

I've never read this mentioned anywhere else before.

[jwjensen356]

Very interesting theory about leaving that resistor in tweeter protection. I am fascinated by the use of #24 wire.

John

[dynaco_dan]

>Very interesting theory about leaving that resistor in

>tweeter protection. I am fascinated by the use of #24 wire.

>

>John

Hi John;

The resistor in series is my guess only, Ken Kantor is the best qualified person on this site to comment with any authority on this thought of mine.

The wire guage is extremely fine, and I will make an attempt to find out the correct size today, being stranded there is not much I can measure.

[jwjensen356]

Dan, while you were in there, did you record the capacitor value (and the type of capacitor?)?

John

[dynaco_dan]

Hi again;

The internal wiring used in the Dynaco A-35 speaker system was, 24 US Guage copper stranded wire, approximately 20 individual strands, pretty tiny.

The entire wire, all 20 strands, is almost the size of a line drawn with a pen.

There is a price difference in different guage wire.

It appears that little was known about cable losses, perhaps.

I do not know if there would be any percieved improvement with a higher quality and heavier guage wire.

Like anything else, if you do all the work of buying and changing the wires, you will hear an improvement, almost guaranteed.

Perhaps upgrading the cap and replacing the resistors with highend?

It goes on and on.

I believe that AR used 18 guage stranded wire in their classic speakers, at least it was on the older dual tweeters.

[dynaco_dan]

Hi John;

I posted that A-35 capacitor and resistor information, post #29, Feb 15th in detail for reference material.

I also had the crossover board in my hand.

[jwjensen356]

Vern, your information is specifically about the A-35. Have you ever poked around in the innards of an A-50? The cross-over network information that someone put on the web shows a 5µf capacitor in series with the tweeter (and a 10µf capacitor in series with a 10Ω resistor across the paralled woofers). Was the use of electrolytics a universal practice in these Dynaco speakers?

John

[dynaco_dan]

>Vern, your information is specifically about the A-35. Have

>you ever poked around in the innards of an A-50? The

>cross-over network information that someone put on the web

>shows a 5µf capacitor in series with the tweeter (and a 10µf

>capacitor in series with a 10Ω resistor across the

>paralled woofers).

.

.

.

Sorry, I can't confirm this at this time.

.

.

.

Was the use of electrolytics a universal

>practice in these Dynaco speakers?

.

.

.

I normaly only saw Jensen caps in A-25's until I saw this A-35 cap, it is Micro brand, it is a different colour, reddy - wine coloured, and glued to the board.

Non-polarized NP electrolytic caps were always used to filter out the lower signals from the tweeter.

There may be two reasons why they used electrolytic caps.

One might be they were cheap.

The other may be that there was not any other inexpensive alternative technology back then.

Today you might find Polypropylene or other caps instead of electrolytics.

.

.

.

Hi John;

I haven't poked around in an A-50 since the early '70's.

I do not want to just look inside mine at this time for curiosity, sorry.

Perhaps at a later date I may just do it for historical accuracy, John.

I just went to see what the different crossover frequency of the A-25, A-35 and A-50, I was not able to locate them in my notes.

My feeling is that the A-25, absolutely for certain, and A-50, maybe, would also be just a cap in series with the tweeter and the woofers using their natural upper roll-off.

The A-10 has a slightly more complex crossover, no adjustments at least, I have seen photos of some, I believe it also has a coil for the smaller woofer.

[dynaco_dan]

>>Vern, your information is specifically about the A-35.

>Have

>>you ever poked around in the innards of an A-50? The

>>cross-over network information that someone put on the

>web

>

>

>>shows a 5µf capacitor in series with the tweeter (and a

>10µf

>>capacitor in series with a 10Ω resistor across

>the

>>paralled woofers).

> Was the use of electrolytics a universal

>>practice in these Dynaco speakers?

>.

Hi again John;

Back again with a little more information.

I went to the, Gregdunn site, a great site to visit, for some more meat, there was no crossover information there.

The google on the web found some information at a site with drawings by, Mr David Dlugos, an ebay seller that I have done business with, and the A-10, less switch and no schematic, A-25, A-35 and A-50 does show also a 1khz xover points, 5 position switch with resistors, 5uf cap for the tweeter, in the A-50 speaker at least.

The woofers show a coil in series, a 10 ohm resistor and 24 uf cap in parallel.

With the extra woofer crossover components they obviously wanted the woofer to cut off at a lower frequency than as in the A-25, for example.

My guess is that the dual drivers and different enclosure design perhaps caused some sort of interference with that area of sound, particularly male voice, output.

Photo 1 is the A-10 cabinet drawing

Photo 2 is the A-25 ditto

Photo 3 is the A-35 ditto

Photo 4 is the A-50 wiring schematic, there is no cabinet drawing yet.

These look better on your computer after you've downloaded them.

They print up a little too much to the left on paper, without me tinkering with the drawings.

It was nice of David to do the drawings, thank you.

After looking at the A-50 tweeter section of the crossover I see a difference in the A-35 board I have.

I will write this up at another time.

They do not seem to be identical.

I believe there may be an error in the crossover drawing.

As I see it, there is a 10 ohm resistor in series with the tweeter at minimum, and the 2.2 ohm in my crossover is not in this schematic which is the minimum for the A-35.

More for me to research in the future for archival accuracy.

Please remember that this is a drawing of the A-50 speaker, not the A-35, I may be wrong.

[jwjensen356]

I'm still getting introduced to my A-50s. I've had them for about three months. I've been playing my old recordings and enjoying them more and more.

Coincidentally I had been doing mild reworking of my old amplifiers, mainly replacing the capacitors. I finally dug into the audio circuitry part and replaced the coupling capacitors. It's hard for me to say I improved the sound but I certainly improved the balance of the output tubes. The balancing (really, unbalancing) was getting to me. Now these three year old 6550s are spot on and stay that way (my new ones can stay in a drawer for a while longer). I just happened to check the bias balancing when I had a recording on that was heavy in the bass. The quiescent value per tube is 65 mA but when the solo tuba came on the value was pegging about 120mA (measured with a DVM). A lot of power was being pumped into the Dynacos, much more so than my old speakers. Yes, I will add the fusing, just in case. But the sound was great!!!

JJ

[dynaco_dan]

Hi JJ;

Please remember this readers and Dynaco classic speaker fans.

You can ALMOST damage a woofer or tweeter.

My experience with 100's of burnt out woofers was mainly with the Dynaco A-25's but all classic Dynaco woofers are similar.

The voice coil form starts to discolour as it is being over driven, and after a while it becomes toasted, just like toast, burnt black and disintegrated.

The Dynaco A-25 woofers heating up in my experience, would start the voice coil insulated coating bubbling, and the bubbles would rub in the gap and sound like a faint speaker buzz to the listener.

At that point it is too late, but back then, they were covered under warantee, if and only if, the adhesive they had used caused a separation of the voice coil from the form.

Doesn't do us much good today, but do not over drive them, that is all.