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Old 12th Jan 2019, 8:52 pm   #1
tin0gauge
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Default Akkord Pinguette valve snakeskin portable

Hello folks, trying to find my way through this lovely radio now I have got the smoothing sorted out, schematic on Radio Museum, it has MW, LW and FM. I get a very low and distorted signal though on MW mostly just ambient noise off my PC etc. The output stage is fine and loud. I have changed the mixer, second and third IF valves and the DAF96, the 1st IF is only used on FM I am sure as the heater gets disconnected on AM.

I am not sure if the DAF96 is used as a detector on AM, it has solid state diodes in the FM discriminator. the signal is coming through the IF stages albeit very low as removing the 2nd or 3rd IF valves loses what little signal is coming through. I think I can get my hands on a signal generator but not sure what sort of signal I need to input at each stage to test the circuits. All the voltages on the valves seem to be OK but too high e.g. instead of 83v on the anodes there is 90v + this may be because the radio is not drawing much current. Any ideas please ? where else can I look for the problem. If I put my finger on the input to the 2nd IF at point No1 on the wave change switch whilst on FM I get an FM type hiss through the radio which may not be relevant.
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Old 14th Jan 2019, 2:22 pm   #2
coopzone
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Default Re: Akkord Pinguette valve snakeskin portable

The voltages may be a clue, try to establish if current is flowing through the valves. perhaps short the g1 to ground and see if the anode voltage changes? check the cachode voltages (if possible) make sure it's not floating up near the anode voltage ie open circuit heater/cachode circuit.

You may be able to get the service sheet from the link at the top of this page. That will give you the correct IF values for AM/FM so you can set your signal generator, probably 460khz and 10.7mhz ? But unless you think the twidler has been at work it's unlikly to be far out.

Check the local oscillator is working ok - if you have access to a scope or frequency counter? Or build a little rf detector from a cap/diode and see if it's generating any rf
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Old 16th Jan 2019, 11:52 am   #3
'LIVEWIRE?'
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Default Re: Akkord Pinguette valve snakeskin portable

To save the OP looking on VRSD, Akkord is not one of the makes listed, at least in the 'Instant Downloads' section, though I note that he says the schematic is on Radio Museum
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Old 18th Jan 2019, 11:30 pm   #4
Chris55000
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Default Re: Akkord Pinguette valve snakeskin portable

Hi!

Nearly all battery valve sets used automatic neg. GB dropped across a resistor in the –HT lead, which for the usual type of output valve used in these sets, is about 470 or 560 ohms, with the –H.T. measuring about –5.5V with respect to chassis or –L.T. line, so a meter test of the voltage drop from –H.T. to chassis divided by the nominal value of the auto–bias resistor should give a rough idea of the H.T. current drain, about 8.5mA to 9.5–10mA on A.M., and about 12–13mA on F.M.

The bias reference point of the output valve is pin 5, which is f(ct) and G3.

Low volume and sensitivity can be caused by partial filament failure of either section in the DL9x output valve, but unfortunately visual examination won't show this, but a quick meter continuity test with a dmm between pins 1/7 and the centre tap on pin 5 will – use the dmm on it's high range (not less than 200k) to ensure you don't overload the delicate filament by testing it on too low an ohms range!

Lack of continuity either pin 1 or 7 to pin 5 means a new output valve!

A.F. amplifier stages use a DAF9x diode–pentode valve operated under starvation conditions in order to provide a high voltage gain, and it's anode and screen–grid resistors are notorious for going very high in value to completely o/c, the best way to check them is to pull out the DAF. . . and ohms test them directly between the A and G2 pins of the DAF. . and the +H.T. battery point, renewing any outside 10% of their marked colour code!

Don't forget that battery valves are fairly critically dependent on correct battery L.T. voltage for adequate performance and lifespan, and there's always a chance somebody could have already badly damaged them from over–running, unsuitable power supplies, excessive L.T. line ripple from unsuitable "battery elimators", etc., etc!

The range of L.T. these valves work from is 1.25 to 1.4V, their filaments are designed for operation from a dry battery whose nominal voltage is only 1.5V for a very short period of time from new – any mains–fed source of L.T. power must be designed to a max. source voltage of 1.4V only!

Chris Williams
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Last edited by Chris55000; 18th Jan 2019 at 11:56 pm.
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Old 18th Jan 2019, 11:45 pm   #5
Chris55000
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Default Re: Akkord Pinguette valve snakeskin portable

Hi!

Sorry I didn't notice the OP mentioned he'd got adequate F.M. volume, therefore it's fairly certain the fault lies with the DK96 MW/LW mixer/oscillator stage!

The DK96 is even more sensitive to correct battery L.T. voltage than the other valves in this series, and it isn't renowned for being over long–lived either!

My recommendation is first of all to check the screen–grid (G4) and oscillator–anode (G2) feed resistors, the G4 feed is about 47–68K and the G2 (osc anode) feed about 27–33K, nearly always series–fed via the MW/LW oscillator reaction feedback coil winding to the valve's G2 pin!

If both G2 and G4 feed resistors test OK and there's no obviously leaky capacitors, please obtain another known good DK96 valve before you go any further!

DK96 pinout:–

1:– f(–), 2:– a, 3:– g2, 4:– g1, 5:– g4, 6:– g3, 7:– f(+)/g5

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Last edited by Chris55000; 19th Jan 2019 at 12:05 am.
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Old 19th Jan 2019, 11:40 pm   #6
Chris55000
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Default Re: Akkord Pinguette valve snakeskin portable

Hi!

Could you confirm which Model you have please - there's about 6 of these shown on RM with valves, mostly all LW/MW/SW and VHF, and there doesn't seem to be any three-band ones (LW/MW/VHF) listed!

Chris Williams

PS!

Their circuits show the DF97 FM RF stage as having in internally connected supressor-grid - this is NOT the case as the DF97 was recommended for tetrode operation with G3 and A connected!

Correct DF97 pinout:-

1:- F(-), s, 2:- A, 3:- G2, 4:- G3, 5:- F(-), s, 6:- G1, 7:- F(+)
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Last edited by Chris55000; 19th Jan 2019 at 11:45 pm.
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Old 25th Jan 2019, 10:34 pm   #7
ocean-boy 204
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Default Re: Akkord Pinguette valve snakeskin portable

Hello,

here is a link to Akkord schematics:
http://www.nvhr.nl/gfgf/schema.asp?Z...sSubmitted=yes

kindly regards
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Old 8th Feb 2019, 3:03 pm   #8
tin0gauge
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Default Re: Akkord Pinguette valve snakeskin portable

Thank you gentlemen for all the advice, I am a novice so going through a learning curve. To recap this is the model with MW,LW and VHF. solid state discriminator but everything else is D - 96 series valves. It has good audio from the vol control. The problem I think is around the AM detector DAC and the 3rd IF DF96. I have tried to put 470kc into the diode input on the DAC but get nothing through, if I do the same with a Pye portable with the same valve line up I can get something through from there but not sure if this is just audio leakage. I get nothing from the grid of the 3rd IF, All the voltages on both valves seem OK but for the anode on the DF which should be at 82v and it is nearer to a 100v. Heater voltages are OK on both and of course I have changed both valves for known good ones. So is the DF conducting ? and should I get an IF signal from the diode input of the DAC ? If it was the detector diode DAC I would have thought the radio would have worked on FM. Thank you for your patience.
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