2050 questions

ggn71

New Member
Hi all,
I just received a beautiful Classic Series 2050 that I bought a couple weeks ago from a Maryland based professional seller who said the unit was working good. Very few details on the unit, whether it has already been restored or left untouched. The tubes appeared to be all original EICO branded, untested though.
These units are pretty rare, especially here in Europe, so I decided to go on and buy it.

Seller's photo

2050-6.jpg

Thanks to the seller and his bulletproof packaging, the unit arrived completely intact. :banana:

All tubes are EICO branded, they all tested very strong on my TV-7/U. Westinghouse 7591, Mullard 5AR4, 7247 and 6EU7. Date 1963-64.
With the bottom cover removed, I can see that this unit has probably never been serviced nor restored.


IMG_4334.jpeg


All original caps, resistors, power cord...
All of the resistors values I checked were within specs, as well as small capacitors.
I removed the filter can caps from circuitry to check for capacity and leakage, they all tested very good being within specs by less than 5%.
I also changed the power cord for a 3-wire one and removed the death cap.
With these basic steps achieved and the unit safe to operate, I checked operating voltages against normal values and the results were pretty good. They didn't precisely match the specified operating voltages, but were still pretty close.
Now hooked to a pair of Cabasse Sloop, the Eico is ready for a listening session.

IMG_4356.jpeg


Level at zero to let the thing warm up, no hum can be heard. From time to time I can hear a faint static noise in both speakers. Once warmed up, I tried a few vinyls and digital music via aux input.
To be honest, as is, the Eico is far from sounding as good as my fisher 400, nor my Tronola modded ST-70.
It is less detailed, lacks bass and sounds somewhat muffled.
From the very little information available I've read about the 2050, I know that it is very similar to the ST-40 and that both are very nice sounding amplifiers.
What do you guys think I should do to get the best sounding experience out of the 2050?
Change PECs for discrete components?
Which values, per 2050 schematic or would ST-40 values be a better choice?
2050:
2050.jpg


ST-40:
ST40.jpg


Would it be also a good idea to change the biasing from cathode bias to EFB? How?
Any inputs from you guys would be greatly appreciated.
:bowdown:
 
Hello,
a little update and a bunch of new questions.
I finally had time to figure it out myself, PECs replacement with discrete components is definitely the way to go.
I will however leave the tone controls PECs in place for the moment, those will need their own little board to be constructed and properly fitted.
What's been done in the last couple days: PC3 and 4 replaced with discrete components, C11, 12, 13 and 14 coupling caps replaced. The amp already sounds much better to my ears!
I ordered the rest of the needed components for PC5 and 6.
I intend to replace both cathode resistors and bypassing caps. Any advice with the replacement values? As per schematic or with different values in order to preserve the output tubes?
Finally, as the phono stage looks very similar to the ST40/70 phono stage, do you guys think I could apply the Tronola phono preamp modification to the 2050?
Thanks!
 
Hi all,
I received my Mouser order today, time to remove those PECs for good.
Attached are a couple pictures to show my work, with is probably not the best looking but is electrically correctly wired.
In addition to what had previously been done, PEC 5 and 6 were totally removed from circuit and replaced by discrete components.

IMG_4402.jpeg


IMG_4401.jpeg


Main operating voltages:
V11 GZ34 336VAC 398VDC, should be 335AC and 425DC.
V7/8/9/10 Pin 3 396V Pin 4 335V, should be 415 and 350.
Voltage drop across cathode resistors 12.8V, same as before resistor replacement. Original resistors measured both 130 Ohms.
I forgot to take the voltage between plate and cathode to be able to calculate plate dissipation.
Plate temperature is 370F, pretty consistent for the 4 tubes.
Should I be worried for the tubes' life?

Now playing :beerchug:

IMG_4404.jpeg
 
After a hour or so of music playing, here are the idle operating voltages again:
Voltage drop across cathode resistor 12,5V
Plate to cathode voltage 368V
With the 125 Ohms cathode resistor, plate dissipation is about 17W for 48 mA idle current.
Could someone confirm that my tubes are safe with this setting?
 
Hey all,
continuing my monologue ;)
after having listened to the fisher 400 for a couple hours, I hooked the EICO up to the same pair of speakers to have a direct comparison in order to find out what is bothering my ears when playing the 2050.
Well it clearly sounds much better than before recapping, but still... something's missing. Mids are a little too present, and it's definitely lazy with the bottom end. Highs are clear and pleasant to listen to, with no listening fatigue associated.
I decided to clean up the signal path, getting rid of balance control (pot was horribly off-track and scratchy), Hi Filter, Tape Out, Tape Monitor. Tape input converted to standard line level input.
Level control input resistors changed as well, the original ones drifted more than 25%...
I then changed output coupling caps from .027 to .1 uF to improve bass response, with slight audible effect at high volume.
As I listen to music 95% of the time at low volume, next step will be to add a loudness switch to the circuit.
I plan to use the HI Filter switch which is now available. Volume pot is not tracking very good, so I ordered an ALPS 500K with loudness tap to be able to wire the loudness circuit into the amp.

IMG_4415.jpeg
 
Anything to add to your thread? How is it sounding now? I have one coming through the mail tomorrow that will need some service work done to it.
 
Thanks for your report. I have a modded ST40 and changing the PECs for discrete components was an improvement. Interesting to hear you’ve had good results with cleaning up the signal path too.

The problem with posting on the Eico forum is that you get less daily tube traffic.

Still, nice work!
 
Hi!
with everything happening all around the world with this virus thing, I think we will all have some time to spend on the internet!
Since my last post, I continued the work on the unit with the following mods/improvements:
- EFB implementation based on Dave Gillespie's work with other cathode biased units (Dave actually helped me a lot!)
- phono circuit mod as per Stephen Lafferty's instructions on how to improve the ST40/70.
- matched quad of brand new TungSol 7591A reissue. (I wanted to preserve my original EICO tubes)
Now the amp runs like a champ, 2 to 4 hours daily. I absolutely love it.
I still need to design the loudness circuit, but I just cannot find a 500K loudness tapped pot which is not way overpriced.

A few pics

part of the EFB implementation

IMG_4660.jpeg


The BIAS adjustments potentiometers

IMG_4666.jpeg


Now playing Louis and Ella :)

IMG_7624.jpg


The glowing TungSol

IMG_7625.jpg


If I can be of any help, don't hesitate to ask.
 
Love the great photos. I am impressed with the work you have put into making the amp sing again.
 
Last edited:
Thanks! This amp has been a pleasure to work with. The best improvement is by far the EFB, which lowers the operating temperatures to a perfect level tube/xformer wise ;)
 
Thanks for your further comments. I've just noticed that you are based in France. Are you using a step down tranformer for the US power transformer?
 
Yes I do. I just checked my wall voltage at 237VAC, the step down transformer brings 119VAC to the unit.
 
Would you happen to have a schematic for the EFB™ circuit you are using? I'm modifying an Eico 2036. THX.
 
here it is
The voltage regulator is a LM337. The schematic is based on Dave Gillespie's work with the Dynaco SCA-35 which is also cathode biased.

upload_2020-3-21_14-58-10.jpeg
 
Some photos of the 2050 I just acquired. Arrived in nice shape, but unpacking it about had me heading for the sofa.
 

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