St 70 on the job

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St 70 on the job

Postby leadtower » Tue Nov 29, 2005 8:49 pm

Hi; I posted some time back looking for info on bias settings for my ST 70 with Shannons board. I was having some trouble getting it to bias properly. Not no more; it is all better now and let me say it sounds ...great. I am playing it through my Altec Valencias, does it get any better than this?
That being said; I wonder can anyone tell me if I should install another pair of bias pots; one for each EL 34?
Also there was a post concerning using 12bh7 in place of the 12au7's; is anyone doing this; because I have some NOS 12bh7's I could try providing it doesn't fry the power trans. However I think I saw some changes suggested if you want to use them.

Also; to Shannon and E.W. and Terry and Thermion; thanks guys, I could never afford to hear music this good in my home if it wasn't for these kits and the help you guys provide. I Have the BB and ST 70 and next up is the Eikes. BTW; what are all you guys using for pre-amps with these amps if I may ask?
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Postby mesherm » Tue Nov 29, 2005 9:15 pm

At present I use Dynaco PAS-3X preamps which I have rebuilt. I have also used an ADCOM GTP-502 and a Velleman 8021, both solid state preamps. All have worked perfectly and had no trouble driving a tube amp.
Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
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Postby EWBrown » Wed Nov 30, 2005 5:48 am

I've used re-built Dynaco PAS-3s preamp,, and currently a Bottlehead FPIII linestage (and Seduction phono stage when I get a turntable).

/ed B in NH
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preamps

Postby TomMcNally » Wed Nov 30, 2005 8:23 am

My favorite preamp/tuner is the SS Adcom GTP-500 II. I bought a couple of them used on eBay. Remote motor driven volume, nice quality. I also have a Dared SL 2000A which uses a pair of 12AT7s and a 5Z4 that lights up the room ... sounds great.
Others in the house include a Heathkit A-111 (I think that's the model) and a Dynaco PAS-3 awaiting rebuild. I have the matching (Solid State) preamp for my Velleman K-4000, currently not working. It's cool because it has a remote, a phono stage, and it matches the amp.
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Re: St 70 on the job

Postby Shannon Parks » Wed Nov 30, 2005 9:13 am

leadtower wrote:That being said; I wonder can anyone tell me if I should install another pair of bias pots; one for each EL 34?


Hi leadtower,

What are you looking to do here? The original Dyna pots provide the channel biasing, while the pots on the PCB provide individual biasing already.

I'll second the Adcom recommendation from Tom. I like the GTP-400 'cause its cheaper than the 500II but without remote. Or is that the 350? I get the GTPs confused.

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Postby EWBrown » Wed Nov 30, 2005 9:27 am

An "overhead" view of one of the ST-70s (with tubes4hifi VTA70 driver board), a Bottlehead "SEX" 2WPC SET amp, and the heavily modded K-502, using 16A8s (in the blue chassis). And a couple of ressurected (de-rusted and repainted) Dyna Z-565s with the PVC insulation leads, waiting for a project to call home... And lurking in back, the front of the "stainless steel behemoth" ST70 using a stainless steel chassis from Uncle Ned a couple years ago. And a set of the infamous "Handwound" power and OP trannies... Off to the left is portion of the remains of the "plinker pile" (originally about 20K of various tubes that were "rescued" from a farmer's barn) Yellow_Light_Colorz_PDT_09

http://www.frappr.com/bottlehead/photo/628464

If that doesn't work then this will:

Image

Not the best photo, things were stacked up to get them out of the way of some serious cellar cleaning...

/ed B in NH
Last edited by EWBrown on Wed Mar 26, 2008 5:53 am, edited 1 time in total.
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Thanks Guys

Postby leadtower » Wed Nov 30, 2005 9:43 pm

I see a lot of Pas 3x's. I have one with the balance/tone bypassed and the new diodes installed. I bought two new boards for driver and phono stage for that pre-amp but have not stuffed and installed them yet. Anyone tried new boards?

Sorry Shannon; stupid question on the bias pots; I get it now. What can you say about the 12bh7's; the thread is a little confusing; makes it sound like you need to make some circuit changes to use them.
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Automotice touch up spray paint

Postby EWBrown » Thu Dec 01, 2005 6:07 am

I use automotive "touch up" spray paint available at any car parts store, I like the metallic red, blue and green colors, and either black or very dark green for the laminations, if they need it. No special techniques, just remove theend bell, clean off any rust - I use steel wool, then perhaps 3 or 4 applications of the spray paint, sanding lightly between layers, if required. For the lams, I use the brush-on touch up paint, that has the bruch in the lid of teh bottles. Spray paint would also work here, with appropriate masking of the parts of the trannie that should not get painted (windings, lwires, etc).


So far, I only paint steel chassis (in additrion to trannie end bells) , as aluminum requires more preparation and priming prior to painting. Otherwise the normal spraypaint just won't "stick" correctly.

If the original bolts holding the trannie end bells are rusted, I'll replace them with new stainless steel or brass hardware. The Dynas Z565s usually have only two bilts holding the bells in place, but they and the laminations are punched so that bolts can be run through at each corner, if so desired. This is a cosmetic, not a functional issue.

Another view: (and testing ImageShack)
Image

Update 25 MAR 2008:

Since this photo was taken, I have replaced the Svetlana EL34s with J/J KT77s, they sound great and needed only a slight bias tweek to get them back up to 50 mA each. Each power tube is individually adjustable - the four "corner" trimpots handle that duty.

The Driver Board is one of Roy Mottram's VTA-70s, which I got before Shannon's ST70 board was available Yellow_Light_Colorz_PDT_02

The Can Cap is there mostly for looks, I ended up using a "cap board" for the PSU, with thoughts of adding in some of the additional capacitance in the multi-section cap, if I though t that it was needed (it wasn't).

/ed B in NH
Last edited by EWBrown on Tue Mar 25, 2008 7:20 am, edited 3 times in total.
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Re: St 70 on the job

Postby Ty_Bower » Mon Mar 24, 2008 12:12 pm

separks wrote:I'll second the Adcom recommendation from Tom. I like the GTP-400 'cause its cheaper than the 500II but without remote. Or is that the 350? I get the GTPs confused.


They're easy to confuse - they all look the same. I've done a little research - here's what I've found so far:

Everything in the "GTP" family has a tuner:
GTP-350: no phono, no remote
GTP-400: phono, no remote
GTP-450: remote, no phono
GTP-500: phono, remote
GTP-502: remote, no phono
GTP-506: remote, no phono, (multi-room unit)

Nothing in the "GFP" family has a tuner:
GFP-345: no remote, phono amp is on optional daughterboard
GFP-555: phono, no remote
GFP-565: phono, no remote
GFP-710: phono, remote
GFP-715: phono, remote
GFP-750: remote, no phono

Someone mentioned the GTP-600. It really isn't the same animal as the "classic" Adcom preamps above. It's in the "home theather" category, with a Dolby Prologic decoder built in (no DD or DTS, though). It does have a tuner and a remote, but no phono input.
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Postby Shannon Parks » Tue Mar 25, 2008 6:23 am

Thanks for this list, Ty. For the record, I've owned two GTP-400s and a GFP-555 (I think there is even a GFP-555 II with a slightly different phono section). My uncle has had three GTP-500 IIs. Great, inexpensive preamps!
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Re: Thanks Guys

Postby Slartibartfast » Tue Mar 25, 2008 7:21 am

leadtower wrote:I see a lot of Pas 3x's. I have one with the balance/tone bypassed and the new diodes installed. I bought two new boards for driver and phono stage for that pre-amp but have not stuffed and installed them yet. Anyone tried new boards?



I bought a pair of pre-stuffed boards for my PAS. I also did just about all the mods to them, listed on the Joe Curico's site. They work good for me. I need to work on getting the hum out of the phono section, once the volume is at 12 O'clock or higher. I will start by using shielded wiring for that. The tone controls, balance, blend and all filters are no longer in the circuit.

The pre amp stage is very quiet.


Image
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Re: St 70 on the job

Postby kheper » Tue Mar 25, 2008 3:58 pm

Ty_Bower wrote:They're easy to confuse - they all look the same. I've done a little research - here's what I've found so far:

Everything in the "GTP" family has a tuner:
GTP-350: no phono, no remote


The GTP-350 was the first Adcom
pre-tuner I ever heard. The highs are
a bit forward, but the detail is excellent.
Fine phono-stage.

http://www.adcom.com/data/manuals/gtp350manual.pdf

GTP-400: phono, no remote


I owned the GTP-400 for a while. The
LED tuner-presets had a nasty habit of
staying lit, so I exchanged it. Otherwise,
the sound was indistinguishable to the
GTP-350.

http://www.adcom.com/data/manuals/gtp400manual.pdf

GTP-450: remote, no phono


My sister owns this. I like the GTP-350
and GTP-400 better. You can sometimes
get the latter 2 for <$100 on e-bay. A
steal.

http://www.adcom.com/data/manuals/gtp450manual.pdf

GTP-500: phono, remote
GTP-502: remote, no phono
GTP-506: remote, no phono, (multi-room unit)

Nothing in the "GFP" family has a tuner:
GFP-345: no remote, phono amp is on optional daughterboard
GFP-555: phono, no remote


Beware of the GFP-555. The first version
got one good review and people snatched
them up like baseball cards. The sound
quality coming from this pre-amp is sterile.

The GFP-555 II is another story. I currently
own this. Fine phono-stage. 2 sets of
outputs. Excellent stereo image and detail. I
think the highs are a bit subdued. Because of
this, the otherwise wonderful pre-amp is a bit
'brown-sounding'. The GTP-350 and
GTP-400 are far brighter.

http://www.adcom.com/data/manuals/gfp555IImanual.pdf

GFP-565: phono, no remote


The GFP-565 was the finest pre-amp made
by Adcom. They call it the 'reference' for
good reason. 3 sets of outputs: bypass, lab,
and normal. A very clean pre-amp.

http://www.adcom.com/data/manuals/gfp565manual.pdf

I rarely use the tone controls on these
Adcom preamps, but the contour (loudness)
button is very precise and helpful.

GFP-710: phono, remote
GFP-715: phono, remote
GFP-750: remote, no phono

Someone mentioned the GTP-600. It really isn't the same animal as the "classic" Adcom preamps above. It's in the "home theather" category, with a Dolby Prologic decoder built in (no DD or DTS, though). It does have a tuner and a remote, but no phono input.
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Adcom pre/tuner history lesson

Postby Ty_Bower » Wed May 07, 2008 5:21 pm

Does anyone know the chronology of the Adcom GTP/GFP series units? I just assumed the GTP-450 was older than the GTP-500 II, but it appears they are the other way around?

During which years did Adcom manufacture which units?
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Postby Ty_Bower » Fri Jul 24, 2009 9:34 pm

...still looking for a good preamp. I picked up a GTP-450 and a GTP-500 II quite a while back. The 450 has a dodgy balance knob, so one channel tends to drop out if you leave the balance dead smack in the center. Turning the knob ever-so-slightly to either side "fixes" the problem, but that bugs me. I shot the knob full of DeOxit a couple times to no avail. It's tough to take the thing apart enough to get a clear shot at the pot. Besides, the 450 has no phono preamp and I do have a turntable.

The 500 II has been working reasonably well for me, but it's awfully noisy. I didn't really notice too much until I got the high efficiency Klipsch, but now the S/N ratio is an issue for me. My amps tend to be really quiet with the inputs shorted, but you hear hiss once the Adcom comes on.

Any recommendations for a nice preamp, not too expensive, remote controlled, and ridiculously good noise numbers?
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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