ST-70 Mods

Postby mozilla » Mon Feb 02, 2004 11:39 am

s2kov wrote:Sir Moz,

Where do you think i can get the mil-spec board to replace the original driver board? How much?



There are 2 options:

1. There is an american-chinese guy who sells these on ebay.

2. Get from joe curcio, its called "Stereo 70 Driver Board (7199 Board) Replacement Module " . It is the same circuit but in a new mil-spec board.
http://www.curcioaudio.com/dynadr_3.htm ... 0AMPLIFIER
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Postby s2kov » Mon Feb 02, 2004 10:33 pm

Sir moz,

Thanks.... Bit pricey pala, is this the one you replace to your driver board?


mozilla wrote:
s2kov wrote:


There are 2 options:

1. There is an american-chinese guy who sells these on ebay.

2. Get from joe curcio, its called "Stereo 70 Driver Board (7199 Board) Replacement Module " . It is the same circuit but in a new mil-spec board.
http://www.curcioaudio.com/dynadr_3.htm ... 0AMPLIFIER
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Postby mozilla » Tue Feb 03, 2004 6:56 am

Yes, from Curcio. The exchange rate was much lower then. I also changed the tube sockets & some of the internal wiring in the process.
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Postby s2kov » Mon Feb 09, 2004 11:43 pm

Sir Moz,

During setting the bias pots at 1.56V, do i still need to connect the speakers for each channel? How frequent do i need to adjust and maintain it?
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Postby setup1 » Tue Feb 10, 2004 1:04 am

What is the purpose of the triode switch for the Hyper modified ST70? Is it a better setting?

reactions are mixed on the use of the triode switch...some like it some don't...some find the triode mode sweeter and mellower in sound at the expense of some dynamics. you also lose out power. i personally prefer the orig penthode, so it's a matter of personal taste


Hi guys!

Just a comment on triode/pentode EL34 operation. I hope when an A/B test between triode EL34 and pentode EL34 is conducted, negative feedback [NFB] is optimized for those two different applications because comparing a triode'd EL34 to a pentode EL34 with pentode optimized NFB is like comparing apples and oranges.

Typically, pentode PP amps have anywhere between 10-20dB of NFB. Merely installing a switch to connect the screen grid to the plate of an EL34 does not guarantee optimized performance for triode configuration because a triode connected EL34 needs much less NFB. 5-7dB of NFB is sufficient to linearize its performance. With 20dB of NFB on a triode EL34, the amp will compress dynamics and constrict the midrange.

Also in terms of actual power, 35W [pentode UL] vs. 15W [triode] isn't really much of a difference in the real world of audio. An optimized triode'd EL34 can actually "sound louder" than in pentode mode because clipping will be softer and distortion will be mostly even order harmonics which are most pleasant to the ears. Scientifically power [watts] and sound pressure levels are logarithmic but the human ear is linear. That's why IMHO the "first watt" always counts in the world of tube amps because who would want a 60W amp wherein the non-linear distortion will just rise exponentially?

May or may not be true but someone once told me that tube life may be shorter in triode mode. Guess the guru's can explain if it were true and how/why so.


That depends, if the B+ voltage on the plate does not exceed the maximum rating of the screen grid [as per tube manual specs on an EL34], then maximum life will not be affected.

Regards,

JE
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Postby mozilla » Tue Feb 10, 2004 6:47 am

s2kov wrote:During setting the bias pots at 1.56V, do i still need to connect the speakers for each channel? How frequent do i need to adjust and maintain it?


Yes with the ICs plugged too. Just set your bias with the amp on idle. Meaning powered on but not playing music.

Normally you wouldn't have to set it often, maybe every 6mos or so. If the bias keeps drifting, a component could be off-spec already.
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Postby rafael montalvo » Mon Feb 14, 2005 1:42 pm

Just some newbie questions: What basic or minimum modifications on a stock ST70 can bring discernable sonic improvements? Is there such a thing as "over modification"? Which sounds better a modified ST70 or a restored one? I am in the crossroad in getting a stock ST70 or a modified one (both having the same price). I sure would appreciate your inputs. Thanks.

Chito M.
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Postby amandarae » Mon Feb 14, 2005 3:33 pm

rafael montalvo wrote:Just some newbie questions: What basic or minimum modifications on a stock ST70 can bring discernable sonic improvements? Is there such a thing as "over modification"? Which sounds better a modified ST70 or a restored one? I am in the crossroad in getting a stock ST70 or a modified one (both having the same price). I sure would appreciate your inputs. Thanks.

Chito M.


IMHO, if your St70 is totally stock, the ff. will give the best "discernable" sonic improvements as you put it in order of hierarchy:
1. Quad cap
2. Bias Board
3. Selenium Rectifier
4. RCA input plugs and speaker output terminals.


2. Get from joe curcio, its called "Stereo 70 Driver Board (7199 Board) Replacement Module " . It is the same circuit but in a new mil-spec board.


I agree with moz,

That is what I got for (the 6922 option type) ages now and never look back :)

Image


I have the in-board Quad Cap module from Curcio also! The original quad cap as can be seen on the picture above is not even connected at all but is there for pure "aesthetics" only. Now, the driver tubes are all 6922's and each channel has two pots (one for each EL-34 tube) for bias adjustment accuracy. Also, I replaced the RCA input terminals with Kimber UltraPlate and the speaker terminals with something like this:
Image
all in all, the mods and part replacements are well worth the money and effort.
cheers!
Last edited by amandarae on Mon Feb 14, 2005 5:38 pm, edited 2 times in total.
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Postby mozilla » Mon Feb 14, 2005 4:18 pm

Nice speaker terminals. Does it include the plate? How much do they cost?
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Postby cia » Mon Feb 14, 2005 5:12 pm

Are those squash balls underneath the ST70?
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Postby amandarae » Mon Feb 14, 2005 5:27 pm

mozilla wrote:Nice speaker terminals. Does it include the plate? How much do they cost?


Yes sir! It includes the plate. See here http://www.diycable.com/main/product_info.php?products_id=531
Before it was only $29.00 so the price went up.


Are those squash balls underneath the ST70?


No sireee! Those are Audioquest Sorbothane Gels with 12.5 lbs maximum load per.

cheers!
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Postby rafael montalvo » Fri Feb 18, 2005 7:51 am

Pardon my ignorance, when you say quad caps you refer to those that are found in the four corners of the board, in amandarae's case they are in orange color. I saw one ST70 with white, others are blackish (I think they are stock). I saw one Stock ST70, with one of the caps showing some bulging. How much do they cost?

I also see some ST70s without the dynakit (dynaco) logos on them, neither on the cage (series 1) or on the body (series 2). Why is this so? Are there such a thing as clone ST70?

Thanks.



Thanks.
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Postby T-Rex » Fri Feb 18, 2005 8:51 am

rafael montalvo wrote:Pardon my ignorance, when you say quad caps you refer to those that are found in the four corners of the board, in amandarae's case they are in orange color. I saw one ST70 with white, others are blackish (I think they are stock). I saw one Stock ST70, with one of the caps showing some bulging. How much do they cost?

I also see some ST70s without the dynakit (dynaco) logos on them, neither on the cage (series 1) or on the body (series 2). Why is this so? Are there such a thing as clone ST70?

Thanks.

Thanks.


Quad cap being referred to is the aluminum canister located to the right of the right bias pot.

The caps you are reffering to on the board are the coupling caps.

Some cages may not have logos as it may have been taken off for one reason or another. For example - the chassis might have been chromed/re-chromed so mapapatungan na yung print or the cage may have been stripped of the logo for repainting of the cage [then the logo got lost].

ST70 is a very popular and succesful amp that many copy it. Yes there are clones [clowns too :lol: ]
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Postby mozilla » Fri Feb 18, 2005 9:57 am

See here http://www.diycable.com/main/product_info.php?products_id=531
Before it was only $29.00 so the price went up.
[/quote]

Nice, CIA, get these na! Drop in replacements w/o having to cut any holes on the chassis.
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Postby s2kov » Fri Feb 18, 2005 3:19 pm

Cloned ST70:

Image
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Postby Killer Mike » Sat Feb 19, 2005 11:32 am

Andy, kelan yung isa? :twisted: :D
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Postby iceman90a » Sat Feb 19, 2005 6:03 pm

Nice Andy! gawa mo yan? :)
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Postby s2kov » Mon Feb 21, 2005 10:05 am

Mike,

Pre, driver tubes pa lng ang na skin. Yung Power Tubes (Quad) next week na daw padating na.

iceman90a,

Nde pre, yung circuit ng driver board plano ko gamitin to compare with the stock.
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Postby rafael montalvo » Wed Feb 23, 2005 7:04 am

Is the clone of the version 1 or version 2? How does it compare (sonically) with the vintage st70? how much would a clone cost? Can you get a clone of the cover(cage) too?
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Postby minicooper » Wed Feb 23, 2005 11:10 pm

Andy, mukhang VTA mod yung driver board. Do you still have plans to pursue the mod?

Cheers!
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