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 Post subject: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 2:16 am 
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Joined: Feb Sun 14, 2021 9:05 pm
Posts: 13
Good evening!

I could use a hand with this one.

We have a VEF Tranzistors radio that has only light static across all bands or dial positions. Also, the volume control has no effect.

https://www.radiomuseum.org/r/vef_vef_t ... xport.html

Does anyone know if VEF ever supplied a board layout diagram for this model? I don't mind working it out from the schematic, but the diagram sure would save on time.

So, I started with the electrolytic caps; some have very high ESR or test open (lifted one leg). These are odd caps. According to the schematic, they only list the capacitance, not the voltage. I was planning on sticking to the original uf value and at around 25V for derating. Does that sound acceptable?

Next, the transistors appear to be germanium PNP type and OEM replacements seem quite rare. Based on the schematic, are there any good substitutions? 9/10 check OK, and 10 lost it's legs due to corrosion. I attempted to solder a single strand of copper wire to the nibs, but it isn't having it! I'll have to replace at least that one, but figured I would order more while I'm at it. Just need to figure out the cross reference...

Very tempted to finally order an Atlas DCA55!

The remaining board components I think I'll leave alone for time being.

Very cool little unit, would love to see it working again. Any assistance is appreciated!

Edit: Transistors are PNP type


Attachments:
radiomuseum-vef-riga-latvia-vef-transistor-tranzistors-export-95766.pdf [491.95 KiB]
Downloaded 28 times


Last edited by pac42 on May Tue 24, 2022 4:19 pm, edited 1 time in total.
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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 3:33 am 
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Joined: Feb Mon 21, 2011 4:19 pm
Posts: 555
Location: San Marcos, CA 92069
Which transistor is bad? Some are easy to replace with silicon transistors with a single resistor change for bias differences.

To sub another germanium, meet or exceed fT and hFE. Unless you are replacing the audio output transistors, Ic isn’t an issue. For output transistors match their hFE and meet or exceed Ic. The oscillator or converter transistor should have roughly the same Cob and Cib or you may need to realign the dial for each band.

Using 25V, 35V or even 50V electrolytic caps is fine. Audio coupling caps are not critical. I often use 10uf to replace 2uf, 5uf and 10uf parts. Bypass caps are also not critical and up to 2X the original value works fine. Use whatever the next higher value is if you can’t roughly match it. A 22uf is fine for a 25uf, and a 33uf or a 47uf would also be a good replacement.

Nash


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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 4:43 am 
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Joined: Feb Sun 14, 2021 9:05 pm
Posts: 13
Hey Nash, thanks for the info!

Pretty sure it's T5.

See photo. Green high-light at upper right corner.

Yeah, I need to bite the bullet and get that semi analyzer.


Attachments:
20220523_223651.jpg
20220523_223651.jpg [ 637.35 KiB | Viewed 621 times ]
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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 5:22 am 
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Joined: Feb Mon 21, 2011 4:19 pm
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Location: San Marcos, CA 92069
T5 is a PNP transistor used for the 2nd IF stage at 465KHz. Many of the old 2SA series transistors would work. You want an fT over 5MHz and an hFE around 40 or more. Something like the 2SA219, or NTE126 would work.

Note that older germanium transistors have a high b-c (Miller) capacitance, and this is neutralized by C67 on the schematic for T5. You will most likely want to remove C67 as newer transistors have much lower capacitance and don’t need neutralization.

The following list may be helpful. Ignore the ones with Ic over 0.2A. Check the datasheet for any you consider to be sure the fT is over 5MHz. Scroll down to see the list: https://alltransistors.com/crsearch.php?mat=Ge&struct=PNP&pc=0.07&ucb=15&uce=0&ueb=1.5&ic=0.015&tj=75&ft=5&cc=5&hfe=40&caps=&r1=0&r2=0&r1r2=0


Last edited by nash on May Tue 24, 2022 6:07 pm, edited 1 time in total.

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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 3:11 pm 
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Joined: Feb Sun 14, 2021 9:05 pm
Posts: 13
Fascinating. I'll get some parts ordered and we'll see what happens. Thanks again!

Right you are: PNP vs NPN - that's what I get for reading schematics on limited sleep...


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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 4:17 pm 
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Joined: May Wed 22, 2013 6:58 pm
Posts: 59
Location: Cincinnati, Ohio
http://www.rw6ase.narod.ru/00/rp_p3/wef_tranzistor.html
"ВЭФ-Транзистор" = ''VEF-Transistor" = ''ВЭФ-Спидола'' = ''Вэф-Спидола-10'' = ''Спидола"
All transistors are Ge pnp.

As for C67 (and C60 for that matter) do not rush to remove it. Like it was mentioned already
it provides positive feedback (regeneration) around T5 (T4 ⇝C60) to compensate (neutralize)
negative feedback (gain loss) through excessive capacitance Ccb of the old and "low max
working frequency" transistors selected. That was typical for all radios in the world in that
period ('50s...'60s).
Excessive C67 value will / may manifest itself by whistle / howl. In this case you will need
to reduce it's value untill it will disappear. At least you will leave / achieve some extra gain
on IF and improve adjacent channel selectivity.

The board layout is in the attachs.


Attachments:
VEF-Transistor brd.PNG
VEF-Transistor brd.PNG [ 506.71 KiB | Viewed 576 times ]
VEF-Transistor brd btm.PNG
VEF-Transistor brd btm.PNG [ 849.64 KiB | Viewed 576 times ]
VEF-Transistor brd connections.PNG
VEF-Transistor brd connections.PNG [ 171.91 KiB | Viewed 576 times ]
VEF-Transistor DC volt and signals.PNG
VEF-Transistor DC volt and signals.PNG [ 191.65 KiB | Viewed 574 times ]
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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 4:31 pm 
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Joined: Feb Sun 14, 2021 9:05 pm
Posts: 13
swam wrote:
The board layout is in the attachs.


Fantastic! Thank you for the layouts!

I will take note on C60/C67. Sounds like an interesting opportunity to experiment.


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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 6:33 pm 
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Joined: Jul Fri 02, 2021 6:20 am
Posts: 89
Location: Ukraine .Odessa
cult Soviet receiver VEF Spidola. also called Spidola with a wide scale.
I have in my collection a few pieces in working order with original parts.
a few diagrams from my archive. maybe they will help you.
it is important to clean the contacts in the range switching drum and in the pads where the transistors are inserted with their legs. they often oxidize.


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20220524_201759.jpg
20220524_201759.jpg [ 2.79 MiB | Viewed 554 times ]
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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Tue 24, 2022 9:27 pm 
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Joined: Mar Mon 17, 2008 5:05 am
Posts: 5811
Location: Ashhurst, New Zealand
I have one of those VEF "spidola" -exported to the UK and marketed through "Comet" stores. Works well, difficult to align with all the coils/capacitors on the turret with no scale! My speaker had the cone disintegrated beyond repair an have never found one the right size and the smaller one I found sounds awful. Interesting moulded plastic chassis and huge battery holders - 6 "D" cells!

Attachment:
DSCF0167 sml.jpg
DSCF0167 sml.jpg [ 185.59 KiB | Viewed 542 times ]

_________________
Cheers - Martin ZL2MC


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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Wed 25, 2022 2:14 pm 
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Joined: Feb Sun 14, 2021 9:05 pm
Posts: 13
majoco wrote:
I have one of those VEF "spidola" -exported to the UK and marketed through "Comet" stores. Works well, difficult to align with all the coils/capacitors on the turret with no scale!


I think one might have to construct an external alignment jig, to get at that drum properly. That does look a little intimidating!

How many radio designs from that era use a drum like this? Was it a VEF design?


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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Wed 25, 2022 2:15 pm 
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Joined: Feb Sun 14, 2021 9:05 pm
Posts: 13
Igor62 wrote:
cult Soviet receiver VEF Spidola. also called Spidola with a wide scale.
I have in my collection a few pieces in working order with original parts.
a few diagrams from my archive. maybe they will help you.
it is important to clean the contacts in the range switching drum and in the pads where the transistors are inserted with their legs. they often oxidize.


Thanks!


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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Thu 26, 2022 7:11 am 
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Joined: Jul Fri 02, 2021 6:20 am
Posts: 89
Location: Ukraine .Odessa
took one out of the box


Attachments:
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20220526_090248.jpg [ 727.79 KiB | Viewed 442 times ]
20220526_084416.jpg
20220526_084416.jpg [ 580.56 KiB | Viewed 442 times ]
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 Post subject: Re: VEF-Tranzistors assistance
PostPosted: May Thu 26, 2022 3:55 pm 
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Joined: Jul Fri 02, 2021 6:20 am
Posts: 89
Location: Ukraine .Odessa
three models of VEF Spidola. on the left is the very first model
"Spidola" (PMP-60, 1960)

"VEF-Spidola" (1962)

"VEF-Spidola-10" (1963)


Attachments:
20220526_174225.jpg
20220526_174225.jpg [ 735.35 KiB | Viewed 421 times ]
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