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Looking for Old Elector Tube Preamplifier article

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stevesebastianb

Member
Joined 2005
qsl.net/vr2xmq
Hi All,

I'm looking for a copy of an old elector article that appeared many many years ago for a tube preamplifier (6 tubes - of 12AU7, 12AT7 or 12AX7?) with a tube rectifier power supply. Unfortunately, I can't remember the year it was published. I remember the main board was quite big, almost A4 in size.

I know it's like looking for a needle in the haystack, but just hoping that this request just might ring a bell with some members?

Regards,

Steve:confused:
 
S

stevesebastianb

Member
Joined 2005
qsl.net/vr2xmq
Elektor Tube Preamp Article - SRPP Design

Dear Yargis & Peter,

Thanks for the response. Yargis, thanks for the heads up and links to Elektor, but unfortunately it was not this design that I was looking for.

The tube preamplifier article I recall was possibbly an SRPP design and possibly appeared in the late 80's to early 90's hence it is not possible to search for on the Elektor web page as their index goes to 1998 only.

I think Peter is correct in referring to the SRPP design, he may be aware of the article that I am referring to.

Regards,

Steve:D
 
O

odermatt

Member
Joined 2005
srpp

If I find it I will post it-by the way my dealer sells a kit with a modified pcb for 149 euro with all prts 6 tubes and poti without power suppy and case!! works pretty well


look at jogi's röhrenbude and there for meine top firmenlinks-there is a dealer called "walter elektronik" who sells kits and I think(I am shure) this is what you are looking for my friend otherwise I will have a look in my files -I also have the original design slights to produce the riaa and line pre on pcb.


kind regards

peter

Ps He has also the input therminal for about 39€ as presented in elektor (all parts and pcb-this is what I use for my projects) helps a lot and comes with a Lorlin 2x6 switch.
 
S

stevesebastianb

Member
Joined 2005
qsl.net/vr2xmq
Elektor SRPP Preamplifier - Feb/March, 1987

Dear Peter & Docali,

Thanks for the information. I have just looked at the link which Docali provided, 100%, spot on! This is the design that I was looking for. Thanks for making my day.

Although I do not understand the German, all I need is the circuit diagrams and the layouts.

Many thanks for your help with locating this one!

Regards,

Steve:)
 
docali

docali

Member
Joined 2004
sphericalhorns.net
You can buy the completely finished amplifier circuit on PCB in germany:
http://www.walter-elektronik.de

Additionally, an appropriate HV PCB is available.

I built this amplifier but made some modifications. I reduced the cathode resistors für ECC81 and ECC82 and did some modifications of the RIAA filter section because I did some Spice simulations with the original circuit and the results were not satisfactory for me. If you are interested, let me know.
 
S

stevesebastianb

Member
Joined 2005
qsl.net/vr2xmq
Elektor Electronics SRPP Preamp

Dear Docali,

Thanks for the reply and the fresh Info. I just sent and email off to Walter Electronics to enquire if they have the HV power supply board for the preamp as this would save me allot of time and hassle.

I actually have the main board built from many years ago and all the chassis work done. The only thing that is outstanding is the power supply and final wiring and I would have it up and running. I dropped the finalization of this preamp several years ago as I fell terribly ill and was hospitalized for several months. It is only now many years later that I found this project stored away in my cabinet and it has re-started my interest.

You guessed it, I was however unable to find the original article and circuits, hence my original post on Diyaudio for help and thanks to you I now have all the details to complete the job started off so many years ago.

Yes I would be very interested to receive details from you of any subsequent modifications you made.

I shall hopefully have this completed within this year. Now to complete the power supply and locate the appropriate transformer. I would like to try and locate a HV "R" core transformer if possible since I have already made so much effort on the rest of it. I have a custom made chassis which looks like a exact replica of an Audio Research cabinet, even the knobs are crafted replicas of the AR knobs. I will not be utilizing the relay switching system in the article as I have opted for some precision "Tokyo Ko-on" selector switches as well as a very high grade "Tokyo Ko-on" volume. All the RCA's installed are high quality "Vampire" RCA sockets. It is a substatial build and once finished I can email some photos if you are interested.

Warm regards,

Steve:cool:
 
S

stevesebastianb

Member
Joined 2005
qsl.net/vr2xmq
Power Supply for Elektor Tube SRPP Preamplifier

Hi Docali,

just thinking about the power supply board of the elektor SRPP tube preamp today, I may decide to go with two seperate rectifier board strips, one for the RIAA and one for the Line Stage. :D

I'm thinking of having two seperate strips for the power supply board with individual heater outputs. The HV rectifier I'm thinking of is the 6Z4 rectifier tube.

Could do SS, but would like to try and have a valve ps if possible.;)

What do you think?:confused:

Regards,

Steve:cool:

P.S. Lite Electronics, China already have a TP-3 (6Z4 tube) ps kit or bare board available. I have the parts so just need to buy the bare boards.:devilr:
 
docali

docali

Member
Joined 2004
sphericalhorns.net
Hi stevesebastianb,

I reduced the cathode resistors of the second stage (ECC81) from 1k to 560 Ohms and the third stage (ECC82) from 1k5 to 1k2. All bypass capacitors are 220uF BlackGate (no parallel foil capacitor). You may try leave the bypass capacitors away as many people say this will yield a better sound but will slightly reduce the amplification factor.

RIAA correction I use is 56k -> 47n - 6k8, 15.6n (orig 18n). Grid resistor of next stage is 470k (orig 220k).

You should shift the heater voltage to about 80-90V above ground (max cathode to heater voltage). This can be done with a voltage devider as shown in the original publication.

A tube rectifier would be worse to test but I can not advise you if a channel separated power supply would yield better results. To decouple the channels you may use clever RC combinations.

Best regards,
docali
 
S

stevesebastianb

Member
Joined 2005
qsl.net/vr2xmq
Power Supply For SRPP Preamplifier

Hi Docali.

Have looked at alternatvies, Lite electronics also have a TP2 HV power supply board which utilizes a IRF830 for the HV section and this could be used for the HV rectification. The heater supply is the usual LM317 supply.

I could run two of these strips seperately for the HV power supply without much problem.:D

Regards,

Steve

:cool:
 
B

bucurb

Member
Joined 2004
grid resistor ...

reinhard,

Grid resistor is part of RIAA correction, absolutely! You are right, but I'm focussing on an other issue. If this grid resistor has greater value (keeping 56K and recalculating only capacitors and one resistor of RIAA network) one could obtain a bigger S/N !

Because Ri + 56K with the grid resitor are making a voltage divisor on the first tube ouput voltage ...
Ri is the internal resistence of the first ECC83 SRPP coupled tube (it seems be about 1K, if I remember correctly).
RIAA correction is applied after dividing first tube output signal tension IMHO.
I wait your opinion, please.

Thank you!
 
B

bucurb

Member
Joined 2004
however ...

Reinhard,

However measured correction (using an anti-RIAA network) of this preamplifier did show closed RIAA curve ... as author wrote in the article.
An explanation may be that ECC83 is working with very low anodic tension (about 150V/0.8mA) being in SRPP, please.

Thanks!
 
docali

docali

Member
Joined 2004
sphericalhorns.net
Hi reinhard,

I would be with you that the RIAA in the original article is is not optimal. The theoretical values ca be obtained from:
http://www.kabusa.com/riaa.htm
R1=47k, R2=6k83, C1=46n5, C2=15n9
The grid resistor of the next stage is part of the RIAA effectively parallel to R1 and not to forget the output impedance of the first stage which is effectively in series with R1! Therefore, R1 has a value of about 56k. Another effect is that the Miller capacitance of the second stage is effectively parallel to C2.

My RIAA values were optimized with Spice using models developed by Norman Koren, thus giving the lowest error I could find with possible combination of standard values of resistors and capacitors.
 
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