Eros2 low voltages (Resolved! woohoo)

blue360cuda · 685

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Offline blue360cuda

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on: April 21, 2024, 06:10:57 PM
Hi, I'm scratching my head and figured I'd ask the professionals for some help here. Built a S.E.X. last year and loving it so decided to try the Eros2 now. Got the whole kit assembled without a hitch. The only "suspect" thing I ran into was assembling the shunt regulator board- there seemed to be a substitution part for the 100kOh 3W resister that wasn't noted in the kit. Pictured in the manual is a grey resister with 100kOh written on it and in my kit I got a pair of brown-black-yellow-gold but that's 100kOh and it measured out so I didn't worry.

All the voltage tests through the build measured within spec.  The resistance test at the end also seemed fine. When I did the final voltage check everything was very very low.


I took the boards off and inspected everything. Nothing looked off, all solder joints seemed fine but I reflowed most of them anyways. I checked all the board components and reflowed those as well. Made sure the transistors had good soldering. You'll have to forgive my memory with this one- during the disassembly, I can't be sure 100%, but I may have originally mounted the red twisted pair going to 22L to D6 instead of D5. I ran through the entire manual double checking all connections and components as well as reflowing anything that looked suspect.

Now the voltage is a tiny bit higher but still very low:

IA / IB 8v DC, OA 5.2v, OB 6.6v, OC / OD 5.4v, OkA 5.5v, OkB 5.6v, OkC 0.15v, OkD 0.41v.

Where should I go next?  I have some extra 6922 tubes if need be but no 12AU7s or EF86. If that woopsie with the D6/D5 swap actually happened could I have fried something? 
« Last Edit: April 23, 2024, 03:42:00 PM by blue360cuda »



Offline Thermioniclife

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Reply #1 on: April 22, 2024, 03:58:50 AM
I must state that I do not have an Eros 2 but it appears that there are 2 transistors mounted backwards on the C4s board. Q1A and Q1C. Unless the instructions say to do that they are probably shot.

Lee R.


Offline Paul Birkeland

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Reply #2 on: April 22, 2024, 04:43:26 AM
Lee is correct that you have some backwards transistors.

The 220 ohm Rc resistors on your rear shunt regulator board are not where they are supposed to be (I see them up on your front C4S board, which should have caused major voltage deviations during testing).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline blue360cuda

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Reply #3 on: April 22, 2024, 05:52:04 AM
Wow thank you both!!!
Good grief, I'm glad to have a set of fresh eyes look it over. Much appreciated!    That being said, can I simply de solder and move these components to the correct positions or did I likely damage something such as the transistors?



Offline Paul Birkeland

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Reply #4 on: April 22, 2024, 06:03:10 AM
I would throw the backwards transistors away and replace them.  The Rc resistors currently on your C4S board are probably fine, but be sure to measure them to be sure they are still within spec.  Your 220 ohm resistors are completely dragging down your power supply and should also be checked, but are probably fine since they haven't caught fire.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Thermioniclife

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Reply #5 on: April 22, 2024, 09:51:20 AM
Indeed a second set of eyes can be very helpful. On my last job of 10 years, I built and tested underwater Navigation systems, brushed and brushless thruster motors, Tremendous lithium ion batteries as well as various sundry electronic items made for US special forces and coalition partners all over the world. I built then, tested them and QC'd them. That was not a good equation for success although I had few problems it concerned me that the company structured this.

Lee R.


Offline blue360cuda

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Reply #6 on: April 22, 2024, 11:50:11 AM
Ordered replacement parts and some extras just in case from digikey. Too bad there aren't any radio shacks or other electronic stores around much anymore.

This'll give me a couple nights to finish my mahogany veneer to match the Thornes TD160 while waiting for parts!

Very much appreciated. First time with the forums and you guys rock!  Now the only questions is which kit to do next?  Leaning towards the 2A3 amp.

Cheers!



Offline Paul Birkeland

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Reply #7 on: April 23, 2024, 04:32:05 AM
What speakers are you running? 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline blue360cuda

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Reply #8 on: April 23, 2024, 04:43:49 AM
I flip flop between my Altec 846b's that I gutted and restored with hot rodded crossovers and my completely stock pair of 604G's in the original Altec 17 cabs.   Both very high sensitivity so they play nice with the 2W SEX and my 2.4W Decware SET El84 amp. Was curious to hear for myself what the buzz was all about with 2A3 and 300B amps.  I should have my parts to fix the Eros2 today but currently I'm running a Darlington Labs phono preamp and the old trusty schiit mani from way back.



Offline blue360cuda

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Reply #9 on: April 23, 2024, 03:41:41 PM
Alright!   Thank you Thermioniclife and Paul!   Got the new parts installed and she passed voltage testing with flying colors.  More importantly, wow this Eros2 sounds fantastic!  The 604s are so revealing and this phonostage is absolutely dead silent and crystal clear. Very impressed! 

So, what's next? 300B or 2A3?   



Offline Thermioniclife

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Reply #10 on: April 24, 2024, 10:00:54 AM
Glad you got it sorted out, my old eyes still work sometimes. Enjoy your new phono pre.

Lee R.


Offline Paul Birkeland

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Reply #11 on: April 26, 2024, 10:43:19 AM
Alright!   Thank you Thermioniclife and Paul!
Thank you for sticking with the debugging process.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man