[BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD

[bernbrue]

You can print out the silkscreen. See first post.
Bernd

 

[brewbacca]

What value of fuse should this use? I'm in the US, but it would probably be good for EU people to know also.

 

[Monoklang]

I'm new into the tube world. And I've been searching around for tubes. Where do you European guys buy tubes? New or old?

I've found this Swedish radio museum selling tubes for these prices:
1  6386: 47€
1  12AT7: 10€
2  6AQ5: 32€
1  EB91: 2,5€

Good?

There are 7 tubes in this STA right? I might have misunderstood the part with solid state power/last 2 tubes...
Do I need the other 2 as well?

I searched for OB2 and 5Y3 but couldn't find them. Are there other names?

Kind regards
John

 

[bernbrue]

Hi John,
The prices for the tubes are quite good, especially for the 6386. You should ask whether the tubes are NOS (new old stock) or used.
There are 5 (6) tubes in this project. We made a solid state power supply so that the OB2 and 5Y3 are not needed here.
The 6386 is a very rare tube and hasn't been in production for quite a long time.  That's why this double triode has been replaced by two pentodes (EF93) wired as triodes. This so called T bar adapter is included on the pcb. In other words: you can either use a single, quite expensive 6386 tube or two EF93 tubes instead.
I would grab the 6386 and the other tubes from Swedish radio museum and build it with 5 tubes.
Hope that helps
Bernd

 

[bernbrue]

What value of fuse should this use? I'm in the US, but it would probably be good for EU people to know also.

250V, 2A Slo-Blo (mouser part#576-0218002.HXP)

Cheers
Bernd

 

[Monoklang]

Hi John,
The prices for the tubes are quite good, especially for the 6386. You should ask whether the tubes are NOS (new old stock) or used.
There are 5 (6) tubes in this project. We made a solid state power supply so that the OB2 and 5Y3 are not needed here.
The 6386 is a very rare tube and hasn't been in production for quite a long time.  That's why this double triode has been replaced by two pentodes (EF93) wired as triodes. This so called T bar adapter is included on the pcb. In other words: you can either use a single, quite expensive 6386 tube or two EF93 tubes instead.
I would grab the 6386 and the other tubes from Swedish radio museum and build it with 5 tubes.
Hope that helps
Bernd

Ok so those 5 tubes are enough then. I'll call the museum tomorrow and check tube status.

If they are used, should I pass or take them anyway?

Thanks.

 

[bernbrue]

Normally used tube are tested. If they are tested "good" you should buy them.
Tube town is a good address for new tubes.
http://www.tube-town.net/ttstore/Roehren:::1.html?MODsid=7ior23l7cgajoaiu69askm4n13

Cheers
Bernd

 

[brewbacca]

Awesome! Thanks!

 

[Matt55]

I am also wondering about the tubes.

Is there certain tubes in the design that you would spend more money on than say others because they affect the sound more or less?

Bernbrue would it be possible to list the exact tubes you used and their prices? It might help others like me who know less about tubes have more understanding!

Thanks, Matt

 

[bernbrue]

Hi,
I can't say it clearer than in the 1st post:

V1= 6386  or 2x EF93 (=6BA6=6K4P-EV)
V2= 12AT7 (= ECC81)
V3&4= 6AQ5 (=EL90)
V5= 6AL5 (=EB91)

Prices are relativ. A new JJ 6386 costs about 110€ here in Europe, used ones are difficult to get. Buy new tubes and you are on the save side. If you don't want to spent that much for a new 6386 tube, buy 2x 6BA6 instead.
Bernd

 

[kml23956]

Has anyone done this or tried it yet?

http://twin-x.com/groupdiy/albums/userpics/6386-Subsitution-Adapter%5B1%5D.pdf

 

[bernbrue]

Yes, I did it and this T bar adapter is already provided on the pcb!!! So buy a few 6ba6 and save some money for buying a 6386 later.
;D
Bernd

 

[brewbacca]

So I've got the build mostly complete and all the boards wired etc. I'm having a lot of issues getting decent signal levels.

1. My output pot only seems effective until about 12 'o clock, and then it doesn't seem to raise the volume at all
I'm using the Edcor with it wired as picture in the gearporn.pdf

2. The input seems quiet, I have to crank it to get decent levels.
I'm using the Sowter 9062 as input and have blue and purple connected, and white not connected to anything. I have Yellow to BRN, Red to BLU, Grey to BLK, and Pink to GRN. Is there a different resistor value I should be using somewhere?

3. Is there a trick to using the simpson meter? I'm able to zero it without problems, but when I crank the input, it doesn't seem to be showing many dbs difference.

4. My voltages from B+ are a little high (325V) and my V+ is low (4.3V). The low V+ seems to be messing with the functionality of the relays. Has anybody else been able to fix the low v+ values if you ran into them?

 

[bernbrue]

Hi
1) output pot is only a 6 dB pad, behaviour seems normal or you've bought a log pot. It needs to be a linear pot.
2) you wired the input transformer the other way round. Just exchange wires " from input tx" with "to input tx"
3) you'll get more gain reduction after you've fixed step two
4) probably a mistake in the V+ psu or the bypass pcb. Disconnect the bypass pcbs and measure voltage coming from Psu. What is the VAC coming directly from the power tx?

What are the voltages at the various measure points?
Cheers
Bernd

 

[brewbacca]

1. I used the pot from the BOM, so I guess it's normal.

2. DERP. Ok, everything that I mentioned seems to be working now.

3. The meter also seems better, but just to double check, do I need a 3.6K resistor in series with it?

4. I don't think anything is in the wrong place, but the 317 in the BOM isn't TO220, so I went and bought an NTE brand one locally. Maybe it's not a good regulator? My AC voltage coming in is 5.69 V, and at the input of the regulator it's 5.98 V dc. The regulator is currently outputting 4.3 V dc. I checked for a short between the regulator and the heatsink, but didn't find one.

Here are my voltages:
A: 58.5
B: 0
C: 1.42
D: 0.722
E: 1.41
F: 0
G: 59.39
H: 110.9
I: 174
J: 0.002
K: 2.75
L: 2.72
M: .002
N: 176
O: 318
P: .143
Q: .005
R: 321.1
S: 214.5
T: 24.69

(By the way, thanks for adding these test points!)

 

[bernbrue]

Well, we are almost done. V+ with 5,98V at the input of the regulator is a bit low. Please check orientation of the diodes D12-15 and D17. What kind of regulator did you use?  You don't need a resistor in series for the meter. The voltages at the test points seem to be in tolerance range . Do you use a 6386 tube or two 6BA6 instead? You have to decide on your own, how smooth you want the compressions to set in. You can reduce R32 in order to lower the threshold so that compression starts earlier. Anyway, you did it, congratulations! Pictures??!
Cheers
Bernd

 

[brewbacca]

Diodes and everything is in the right place. I used the NTE brand 317 but took that out this weekend after some better parts arrived. I put a fairchild LM317 in and replaced the diodses and was able to get slightly better voltage, but it goes down again when I hook up the lamp. The relays seem to be working in any case. Also added a 1W 1K trim pot for the H-Trim to try and get the 325 V down, but it didn't seem to help much.

I used two 6BA6 tubes.

Here's some pictures! I didn't plan the layout as well as I would have liked, so the wiring is kind of a mess. I used the case from Frank.

EDIT: I fixed the loose ground wire on the main board B+ connection.

 

[bernbrue]

Very nice build. You've provided a bypass switch as well, great. I hope you like what it does.
Cheers
Bernd

 

[porkyman]

can i ask a couple questions.

R2 (Bias Board) says 1% on the bom but the part # is 5% and mouser doesnt have a 220 1%  right now. is 5% ok?

i dont understand the different voltage options for ex: v+red =  24v, 12v, or 5v. im a little lost there.

v+red 24v calls for a 4.8k  1/4w but the part# comes back 34.8k . which one is right?

cx2 . im totally lost here. 100 - 220 nf.  is this transformer dependent or does the value not matter as long as its between 100 and 220 nf?

thanks

 

[bernbrue]

Hi,
You can take a 5% tolerance resistor here, but mouser has got a 220 Ohm 1W, 1% resistor in stock as well, which you can take instead.  The red LEDs on the psu need a resistor in series. The value of the resistor depends on the secondary voltage of your transformer.  For 24V you need a 4,8 K resistor, for 12V a 2,4 K and for 5V a 100R resistor.
Sorry, where did you find Cx2? Main board, psu, bias psu?
Cheers
Bernd