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    hello, im new to the forum.

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    dmagazz

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    hello, im new to the forum.

    Post by dmagazz on Wed Jun 20, 2018 10:04 pm

    i have questions, and have also a barn of sorts st-70 that appears to be ALL original to me(dynaco tubes and all). it WORKS, is quiet and clean sounding Smile
    cant post pics yet i guess.
    OK....SO
    my first question is, how loud is an ST-70's 35 watts?

    here is a comparison, my laptop is my music preamp, and being at 60 percent vol into a harman kardon 730 (SS 40 watts)-with both the bass and high on 60%, and the volume on 30%,with a pair of 4 way 4 ohm speakers. it results in about the same loudness as going straight into the st-70.(using the same speakers!) is that ceiling low?or is it me.i might add its still clean at that level.
    but i was hoping and expecting much for more output,

    so i also ask can that output increase with new caps,tubes,and diodes for the recto.
    or do 4 ohm speakers somehow usually result in a lower output by nature?

    another question is how can i figure out the date on this, the bios pots are stamped on the side, and i only saw 1 number,E09373(part number?)
    the cornell dubilier part number UPN 10474 525v quad cap has a 4 digit at the bottom (6642)is that a date of 66?,
    the power tranny has a white number stamp of PAO66.. is it safe to say the dates match? or is that not a date on the tranny.

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    j beede

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    Re: hello, im new to the forum.

    Post by j beede on Thu Jun 21, 2018 1:29 am

    Hello dmagazz,

    The ST-70 has a fairly high input impedance so your computer sound card/AC-97 output may be able to drive it directly. If you are running the same laptop output into the AUX input of your Harman Kardon receiver that signal is passing through an additional stage of amplification ahead of the power amp section. I would expect the receiver to exhibit higher gain in that case--as you are experiencing. I believe that the HK 730 has a preamp output accessible from the rear panel. You could drive the ST-70 input using that pre out to see if you prefer that (more conventional) configuration.

    FYI: The ST-70 puts out less than 35W per channel when measured using the methods used to spec the HK receiver at 40W.
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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 7:36 am

    thanks j beede, i figure the same about the st-70's input.i go straight in, started at a low vol, came up to 60%(same level i set equal comparing the aux to the fm vol going into the aux on the HK730)
    what i did was bring the tuner of the fm on the hk730 up, and turn the vol on my laptop up to that level, switching from aux and the tuner for comparison, thats where 60% vol comes in.
    i figured by doing that im at a comparable standard level, into the aux for the hk730 to have a fair comparison.
    the headroom is seeming very small.
    maybe what ill do today,is run the preamp from the HK730 into the st-70, and see where the vol control is in reference to the vol with the hk730 was.(i have a db meter).id expect it to be around 40% or so(10% give or take)higher given 5 watts less in power.
    i understand the wattage is 5 watts lower on the st-70, BUT the difference in headroom is far lower that it should be i think. for only 5 watts difference. vol is at 30% on the hk730, and the level in to the st-70 was approaching the ceiling to catch up to 30% vol on a solid state unit.
    id expect a tube amp to be much more louder than solid state,given the small difference in wattage, maybe bringing them near equals in volume.
    by the way,the aux input impedance is 30 on the hk730 and the sensitivity is 150mv

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    Peter W.

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    Re: hello, im new to the forum.

    Post by Peter W. on Thu Jun 21, 2018 8:17 am

    http://home.indy.net/~gregdunn/dynaco/components/ST70/index.html  

    Start here with the basic specifications.

    It also helps to understand that Tube Amps are constant-current devices such that power output does not increase or decrease with speaker impedance. With that in mind, comparing a solid-state amplifier to a tube amplifier can be a misleading exercise unless one understand exactly what is going on.

    Here goes:

    a) Your HK-730 is rated at 40 wpc/rms @ 8 ohms.
    b) As it is a solid-state unit, that means it will put out approximately 80 watts at 4 ohms.
    c) You have not given a speaker brand or efficiency, but suffice it that the difference between 35 watts and 80 watts is >3dB under any conditions.  

    In addition, tube amps clip very softly, as OPTs do not pass DC. To some ears, clipping = loud as that is typically what happens when the volume is turned all the way up and/or the signal has a low peak-to-average.

    1.3V RMS will drive the 70 to its full output - what that means is if a pure sine-wave at 1,000 Hz is fed into the 70, it will deliver 35 watts to the load, whether it is 4, 8, or 16 ohms. Were that load to be a conventional speaker, it would burn up in short order if fed a pure sine wave at 35 watts. Musical signal is _NOT_ a sine wave, but speakers and amplifiers have to be rated somehow.

    Which gets into peak-to-average. Generic "Heavy Metal" music has a p/a of about 10 dB. Meaning the loudest passages are only twice as loud as the average. Also true of most folk, & R&R, with some considerable exceptions. However, most (well-recorded) classical music has a p/a of 20 dB, with some as much as 30 dB (Saint-Saens Organ Symphony being one example).

    NOW - let's get into Headroom: If you are driving your speakers at 1 watt, average, and you are playing most non-classical music, an amplifier with 30 watts of power and an 80-watt peak will do fine with only 10 dB of p/a.

    If you are driving your speakers at 1 watt, average, and you are playing most classical music, you will need 100 watts of peak. The HK will clip harshly and sound "loud", the 70 will clip softly and sound soft.

    Forget a 30 dB peak, you would need 1,000 watts for that.

    The above is very broad-brush, with much detail either left out or ignored, but covers the very basic elements.
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    Peter W.

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    Re: hello, im new to the forum.

    Post by Peter W. on Thu Jun 21, 2018 8:31 am

    Please note the interpolations

    dmagazz wrote:i have questions, and have also a barn of sorts st-70 that appears to be ALL original to me(dynaco tubes and all). it WORKS, is quiet and clean sounding   Smile
    cant post pics yet i guess.
    OK....SO
    my first question is, how loud is an ST-70's 35 watts?

    Please read my much longer previous post on volume, headroom and such-like.

    here is a comparison, my laptop is my music preamp, and being at 60 percent vol into a harman kardon 730 (SS 40 watts)-with both the bass and high on 60%, and the volume on 30%,with a pair of 4 way 4 ohm speakers. it results in about the same loudness as going straight into the st-70.(using the same speakers!) is that ceiling low?or is it me.i might add its still clean at that level.
    but i was hoping and expecting much for more output,

    so i also ask can that output increase with new caps,tubes,and diodes for the recto.
    or do 4 ohm speakers somehow usually result in a lower output by nature?

    another question is how can i figure out the date on this, the bios pots are stamped on the side, and i only saw 1 number,E09373(part number?)

    Those part-numbers are not date-related. Dynaco used a number of pots from a number of suppliers. That stamp is the Dynaco P/N and remained the same.

    the cornell dubilier part number UPN 10474 525v quad cap has a 4 digit at the bottom (6642)is that a date of 66?,

    Yes - that is a 4-digit code, the first two are the year of manufacture, the last two are the week within that year. So, the 42nd week of 1966. That cap could be in the system for a long time before it got into that amp, however. So, as late as 1968 could be possible.

    the power tranny has a white number stamp of PAO66.. is it safe to say the dates match? or is that not a date on the tranny.

    That is the Dynaco part-number, not a date code. Are the leads cloth (early) or PVC (late)?  That amp was made from 1959 through 1989, sold as a  stock item through about July of 1990.



    Last edited by Peter W. on Thu Jun 21, 2018 8:33 am; edited 2 times in total (Reason for editing : Getting the dates right!)
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    Bob Latino
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    Dating Dynaco tube amps by using the bias pots

    Post by Bob Latino on Thu Jun 21, 2018 9:44 am

    dmagazz wrote:

    another question is how can i figure out the date on this, the bios pots are stamped on the side, and i only saw 1 number,E09373(part number?)
    the cornell dubilier part number UPN 10474 525v quad cap has a 4 digit at the bottom (6642)is that a date of 66?,
    the power tranny has a white number stamp of PAO66.. is it safe to say the dates match? or is that not a date on the tranny.


    Yes - You can sometimes date Dynaco tube gear products by using the bias pot codes .. See the photo below which shows three cases of bias pot codes seen on Dynaco tube amps. The top bias pot is from a Dynaco ST-70 and the bottom two came from Dynaco Mark III's. The 137 is the EIA manufacturers code for who manufactured the item. In this case, the "137" refers to Chicago Telephone Supply (CTS). The second two numbers (or single number) refers to the year of manufacture. In the top photo the "64" refers to 1964. In the bottom two photos the single number "9" and "8" refer to 1958 or 1959. It can't be 1948 or 1949 because Dynaco did not come into existence until 1955. Could those single digits be 1968 or 1969 ? I don't think so because all the older Dynaco ST-70's that I have seen from the middle and late 1960's had bias pots similar to the top photo with SEVEN digits. The last two digits refer to the week of manufacture for that year. The first pot was built in July of 1964, the second in December of 1959 and the last one February of 1958.

    Bob


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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 1:45 pm

    thanks bob,and peter w the replies
    bob, my pots resemble the post through indented cover style and are stamped on the side, i didnt see a number outside of the part number,come to think of it. i didnt see a value!. i will take a closer second look.

    peter w, thats some serious technical insight right there, thanks.

    my speakers are a custom desighn 4 way design, with 1-100 watt nominal 12 in sub, 1-60 nom watt 6 in driver, 1-35 nom watt 3 in mid, and 1-35 nom watt 3 inch cone tweeter, a variable vol control for the high drivers and a crossover network inside splitting up the frequencies, at the leads the measurable resistance is 3.8 ohms, so i guess its safe to say its about 3.8 ohms and can handle up to 200 watts
    i ask about the reference you gave "the difference between 35 watts and 80 watts" isnt a dynaco st-70, 70 watts by 2, as the HK730 is 80x2 making the reference for the hk730 40 watts not 80?
    so aren't i comparing 35 watts to 40 watts(per channel) not 35 to 80. or was that a typo.

    im starting to wonder(as i havent checked)if the previous owner bios'ed it on the light side for longevity, and is possibly why it seems to be only the power of a 15 watt amp.

    a little more basic info,some irreverent.
    the transformers have cloth leads
    the selenium rectifier is still in use
    all the original dynaco tubes are in use
    as is the capacitors.
    and thanks for helping me determine it is a 66.
    the feet are a round bubble type, not the taller standoff type.
    the cover is brown, however has the "dynaco" plate, not the "dynakit" plate.
    the wires are black and all mounts are screwed,not rivitet(making it a kit for sure)
    there is no pitting in the stainless.
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    Peter W.

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    Re: hello, im new to the forum.

    Post by Peter W. on Thu Jun 21, 2018 2:15 pm

    More interpolations

    dmagazz wrote:thanks bob,and peter w the replies
    bob, my pots resemble the post through indented cover style and are stamped on the side, i didnt see a number outside of the part number,come to think of it. i didnt see a value!. i will take a closer second look.

    peter w, thats some serious technical insight right there, thanks.

    my speakers are a custom desighn 4 way design, with   1-100 watt nominal 12 in sub,   1-60 nom  watt 6 in driver,   1-35 nom watt 3 in mid,    and 1-35 nom watt 3 inch cone tweeter, a variable vol control for the high drivers and a crossover network inside splitting up the frequencies, at the leads the measurable resistance is 3.8 ohms, so i guess its safe to say its about 3.8 ohms and can handle up to 200 watts

    OK, stop there. 3.8 ohms nominal, meaning from about as low as 1.4 to as high as 10 ohms - the difference between impedance (frequency dependent) and resistance (fixed).

    i ask about the reference you gave "the difference between 35 watts and 80 watts"  isnt a dynaco st-70, 70 watts by 2, as the HK730 is 80x2 making the reference for the hk730 40 watts not 80?

    No. The 70 is 35 + 35 per channel, not 70 per channel.  The HK730 is rated at 40 per channel into 8 ohms, giving a theoretical 84.2 per channel into 3.8 ohms. Solid-state amps are a constant-voltage devices giving a theoretical doubling of output watts with each halving of impedance. Tube amps are constant-current devices, putting out a fixed wattage at each impedance as matching the OPT windings.

    so aren't i comparing 35 watts to 40 watts(per channel) not 35 to 80. or was that a typo.

    Not a typo. What you are actually comparing due to the different natures of the two beasts.

    im starting to wonder(as i havent checked)if the previous owner bios'ed it on the light side for longevity, and is possibly why it seems to be only the power of a 15 watt amp.

    a little more basic info,some irreverent.
    the transformers have cloth leads

    Older version, then

    the selenium rectifier is still in use
    all the original dynaco tubes are in use
    as is the capacitors.
    and thanks for helping me determine it is a 66.
    the feet are a round bubble type, not the taller standoff type.
    the cover is brown, however has the "dynaco" plate, not the "dynakit" plate.

    Jefferson Street, then.

    the wires are black and all mounts are screwed,not rivitet(making it a kit for sure)

    Not necessarily. Until Dynaco moved to Jefferson Street they did not have a factory of any nature. "Factory Built" amps were assembled by Drexel Students on piecework. What they had for tooling would be a matter of individual preference. Some would have had rivet guns, some not. Some would have used color-coded wires, some not. That practice continued in a small way well into the Jefferson Street era. If the amp has a serial-number sticker, the odds of it being 'factory' (at whatever level) go to over 90%.

    there is no pitting in the stainless.

    Nickle-plated mild steel.
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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 2:38 pm

    peter w, thats what i implied in saying!
    "so aren't i comparing 35 watts to 40 watts(per channel) not 35 to 80
    because you previously said
    c) You have not given a speaker brand or efficiency, but suffice it that the difference between 35 watts and 80 watts is >3dB under any conditions.

    i initially thought you were referencing the dana at 35, and the hk730 at 80
    but you were referencing power and peak weren't you. i just realized that now.
    sorry for the cofusion.
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    Peter W.

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    Re: hello, im new to the forum.

    Post by Peter W. on Thu Jun 21, 2018 2:49 pm

    dmagazz wrote:peter w, thats what i implied in saying!
    "so aren't i comparing 35 watts to 40 watts(per channel) not 35 to 80
    because you previously said
    c) You have not given a speaker brand or efficiency, but suffice it that the difference between 35 watts and 80 watts is >3dB under any conditions.  

    i initially thought you were referencing the dana at 35, and the hk730 at 80

    OK - just to be sure as this is often confusing until it becomes well understood.

    Your speakers are "seeing" 80 watt rms per channel from the HK730 as they are (nominally) half the impedance of its base rating (40 watts rms per channel). The HK does have a decent power-supply, and so is most likely able to make a 160 watt peak without clipping.

    Your speakers are "seeing" 35 watts rms per channel from the 70, with an 80-watt peak.

    Remember, *CONSTANT VOLTAGE (solid-state) vs. CONSTANT CURRENT (tube).


    but you were referencing power and peak weren't you. i just realized that now.
    sorry for the cofusion.
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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 3:21 pm

    right, i guess this is why we can change the ohms and power of speakers with tube, but it doesn't effect the amp the same in a SS environment?

    it sounds better..
    i put the bios to 1.56, with the amp running music at a decent level.
    also i noticed the bios went down to 1.54 when i cut the signal to the input
    is this ok? a good idea?
    (playing steely dan aja ) Smile
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    Peter W.

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    Re: hello, im new to the forum.

    Post by Peter W. on Thu Jun 21, 2018 3:28 pm

    Not to worry.

    Do consider getting rid of that selenium diode, and doing the resistor mod on the bias voltage. That will help with stability.
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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 3:32 pm

    will do, absolutely!
    i just hooked up the hk730 pre out to the inputs of the st-70
    Smile yes!!! amazing Cool
    thanks
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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 3:51 pm

    ohhh good god, im not sure i can handle this greatness!!
    im goin to jail.lol
    my neighbors will all ban against me now
    Smile stormy monday live by cream ...YAAAAZZ! Smile

    ok i gotta stop, i wanna safeguard this thing before a recto reck's my situation.
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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 4:20 pm

    so now, i played some music at some serious volume.for about 30 minutes now, i rechecked my bios, its 1.4 left and right now.
    it was 1.56 30 minutes ago,
    is this telling me something?

    StevieRay

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    Re: hello, im new to the forum.

    Post by StevieRay on Thu Jun 21, 2018 4:31 pm

    Yep, if that selenium rectifier blows, your significant other, or your dog and cat, or anything else living in the house will throw you and the amplifier out for stinking up the place with toxic fumes...... lol!
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    dmagazz

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    Re: hello, im new to the forum.

    Post by dmagazz on Thu Jun 21, 2018 5:06 pm

    but i dont wanna turn it off..... Sad lol
    i guess ill have to hook my hk730 back up........for now.
    i guess im gonna get what i need straight away,when i am done with this text.
    resistor mod, and bye bye selena

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