mute relay

hi guy's
i have another quick question, what is the voltage of the mute relay in rockola 41710-a / 36196-a amps and is a replacement part available, i believe it is DPST relay. the relay is part number 33263 as in the manual, thanks

cheers
bopper

Hallo Leute
ich habe noch eine kurze frage, was ist die spannung des stummschaltungsrelais in rockola 41710-a / 36196-a amps und ist ein ersatzteil erhältlich, ich glaube es ist dpst relais danke

Prost
bopper



3 mal bearbeitet. Zuletzt am 27.06.19 09:51.

The mute relay is supplied from the 28V rail. 24VDC coil should work. Type is DPST, both contacts are normal open. I don't know a perfect replacement type, note that parameters like coil resistance and hold voltage influence the un-mute timing in this circuit, so better try to save the original relay. (should be the goal anyway)
Regards Jürgen

Hi Jurgen

thanks for the info. i will try to save the relay, trouble being the thin gauge coil wire has broke where it leaves the coil with not much room to solder an attachment wire but i will have a go, another question do you have any details on the diode (rectifier in manual) it is connected to one of the n/o contacts on the
mute relay as far as i can make out the part is k-f-1203, e45-c150 made in Germany, rockola part 33263
while i have the amp out of the box i would like to replace it i presume a suitable Scottky diode would be ok, thanks for help

just done a resistance test across the coil 1.4k

cheers
mick

Hallo Jürgen

Danke für die Information. Ich werde versuchen, das Relais zu retten. Es ist problematisch, dass der dünne Spulendraht an der Stelle, an der er die Spule verlässt, gerissen ist und nicht viel Platz zum Löten eines Anschlussdrahtes hat in manual) wird es an einen der n / o kontakte am angeschlossen
stummschaltungsrelais soweit ich das teil erkennen kann ist k-f-1203, e45-c150 made in germany, rockola teil 33263
Während ich den Verstärker aus der Box habe, möchte ich ihn ersetzen. Ich gehe davon aus, dass eine geeignete Scottky-Diode in Ordnung ist. Danke für die Hilfe

Prost
mick



1 mal bearbeitet. Zuletzt am 28.06.19 07:41.

E45-c150 is a selenium rectifier, 45V, 150mA. It can be replaced with a standard silicon diode (1N4001 or similar).
It should be in series with the coil of the relay

thanks for the info and diode required Marc ,big help

regards

mick

i have managed to solder a wire to the short end of the relay coil and i applied 24dc and the relay operates ok ,i will change the diode with the part 1N4001 as Marc mentioned. I did source a replacement relay with a similar spec as the orignal ,coil resistance 1440 ohms 24vdc but now the orignal ok no need to bother


cheers

mick

I would be curious to see the hold voltage of the two relays. If you have not put it back in the amp yet, maybe you could do a quick measurement.
Just slowly reduce the voltage from 24V to the point when the contacts open.
Thanks Jürgen

i did the test on the stock relay reduced the voltage from 24v and the relay only released when the voltage was as low as 7.4v, i tried in reverse from zero voltage the relay energised at 17.2 v .i was suprised at it holding in at such a low voltage, i am not sure of all data on the aftermarket relay but i will check

now looked at the data it is dpdt but the slight problem it is PCB mount,coil energises at 16.8v,operating time 7ms relase time 2ms

cheers



1 mal bearbeitet. Zuletzt am 30.06.19 09:47.

Hello Mick,
the minimum turn-on voltage of the relay is not a concern in this circuit. When mute is switched on, the coil sees immediately around 28V through the diode and the 250uF cap. will be fully charged through the 220Ohm resistor. When mute is turned off, the cap. discharges through the coil and the contacts open when the hold voltage is reached. With your measured numbers, this should be approx. 0,5sec after the switch. I did not make any measurements when I did my1484 (just replaced the 250uF cap. and cleaned the relay contacts) - that`s why I am curious how this works in detail.
I think the important parameters for a suitable replacement of this relay is the nomimal DC voltage, the coil resistance and the hold voltage.
Regards...Jürgen

Hi Jurgen
i also replaced the 250uf cap with a 270uf 63v and think i may replace the diode tho the original tests ok
the forward bias is 0. 895 v which is a little higher than for a silicon one but i don't know the specs for the
E-45 c-150 original, i may get hold of a replacement relay just to do some bench tests and check results

cheers

mick

Hello Mick,
I used a 220uF and could not see (hear) a problem. However I have not measured my relay so I don`t know the timing I got. The influence of the diode is neglectable unless it has significant leakage current. If we assume that your relay measurement is representative (1440Ohm/7.4V), the calculated value is about 0.5ec.
+- 20% should not be a problem I would think. Maybe some followers of this thread know a spec. on this...
Regards...Jürgen

Hello Mick

I think the only important feature besides the coil voltage is the duty cycle. This should be 100% because the coil must be energized most of the time (as long as no disc is playing). Attract time and delay time are of little importance. The capacitor causes an extension of the delay time. As a result, the amplifier is only turned on when the pulses by switching off the gripper motor and the reset coil are over. The duration of the delay is not important because the pulses last only a few milliseconds.

Best regards - charly49

Hi Jurgen , Charly49
thanks for input, will using the 270uf cap with the slightly uf make any difference to the mute operation or like Jurgen would it be better a lower uf, so reading what Charly say's the relay is energised with the contacts closed until a selection is made and a record is ready to play, i think !

cheers

mick

Hello Mick,

agree with Charlie49, a relay capable of 100% duty cycle is required since the coil is energized as soon as the -28V supply is turned on by the play control relay and remains on until the record starts to play.

Concerning your question if 220uF or 270uF is the better choice, I would say it does not really matter as long as you don't combine the higher capacitor value with a new relay that has significant higher coil resistance or lower hold voltage which would both increase the delay time even more. I have 1 or 2 records in my box where the amp. is un-muted slightly after the first beats although the set-down position of the tonearm is adjusted correctly. The picture shows you what's going on when the gripper stops. Just before, switch#3 was energizing the mute relay and charging the capacitor. When the switch opens, the delay time starts. The diode prevents that the cap. is discharged additionally through the reverse relay coil/gripper motor. Muting starts again immediately with the tonearm switch or manual cancel switch closing.

If you pull the mute connector from the amp. and play a record, you can hear all the noise this circuit cancels.

Regards Juergen

Hi Jugen
if the relay coil is energised when the power is on, it therfore could be on for long periods between any selections being made ,does this not cause temperature problems in the winding of the coil?,thanks for the schematic, is it in the rockola manual for these models (1484/ 430 etc) as i cannot find the page in my copy,if a replacement relay had a lower resistance than the original in this case mine was 1400 ohms could a resistance of suitable value, to bring the replacement to this value (1400) be added in series with the coil?. When i removed this amp i relpaced it with a spare amp temporary which seems to do the same as yours on certain records the mute does not release at the inital start of the record tho the tone arm is set correctly, i will try removing the connector as you suggest and let you know results

regards

mick



1 mal bearbeitet. Zuletzt am 01.07.19 21:11.

Hello Mick,

again, I recommend to keep the original relay if possible.

Duty cycle: The relay is turned on after a selection is made, so several seconds while the magazine turns and switches off after the gripper is finished. New general purpose relays in this size have 100% duty cycle unless otherwise noted, so don`t worry.

Coil resistance: 20% more or less is not a problem but be aware of the influence to the discharge time
Higher resistance > longer un-mute time
Lower hold voltage > longer un-mute time
Higher capacitor > longer un-mute time.
If all changes go in the same direction you could end up with significant longer delay time and you will get more and more records to start late.

The picture is from my 1484 manual, should be same or similar in yours. On some amps, the relay contacts shorten the output, later models shorten the signal after the pre-amp but this has no relevance for the timing.

Regards..Jürgen

Hi Jurgen
thanks for the full explanation, i am going to stick with the stock relay ( thanks for advice on this) now i have soldered the coil wire it seems ok , i will replace the diode and then put the amp back in the box
and test that it's workig ok, i will post after testing, thanks again to you and Charly49 for all your help
it's very much appreciated

best regards

mick

Jurgen
please clear this for me, on the drawing in your post there is the 28vdc line going to - side of the cap
and grd going to +anode side of diode via micro switch 3 when contacts close, on a bench test by connecting the dc voltage this way the relay does not close, with the connection reversed + to diode anode
grd - to relay (cap - side) relay operates with a slight delay to open after power off ( is this cap discharging) i am probably wrong but it is best to ask

cheers



1 mal bearbeitet. Zuletzt am 02.07.19 12:12.

It`s (-)28V, positive ground in the box! Unusual and confusing, I agree.
When you disconnenct the supply voltage, you see the discharge of the cap, the relais opens when the hold voltage is reached. That`s exactly how the circuit works. By the way, the cap. is charged to the peak voltage (sqrt2*28V). So time gets a bit longer compared to measuring it outside with a 28V DC supply.
Regards...Jürgen



1 mal bearbeitet. Zuletzt am 02.07.19 14:01.

Hi Jurgen

thanks for explaining the circuit, it is hard to think grd being the positive side when you have always thought grd as the - side of a circuit, so thanks for clarifying the circuit and all the help with this, ,i wil re-install the amp probably at the weekend i will let you know reults

take care
regards

mick

Ground is a reference point for all voltages. In telecommunications equipment, american cars up to the fifties, british cars up to the seventies, ground is often positive. All measured voltages are negative.
In modern equipment you often find symmetrical voltages, with ground in the middle.
A push-pull solid state amplifier uses at least 2 voltages. With ground as reference, you can measure -40V and +40V for example, and 80V between those two points.

Hi Marc
thanks for your post, me not being into electronics tho i was an electrical contractor the installation
of electrical work is totally different, so i am trying to get my head around what you all explain , with the + side being ground which i now understand, i think my problem is when i look at the amp (34725-A) schematic, now knowing the grd polarity and seeing the electrolitic caps with - side down to grd and + end
to the - side of the voltage , i will grasp it with all the help i get from yourself, Jurgen and Chary49


cheers



1 mal bearbeitet. Zuletzt am 03.07.19 11:22.

Hi Mick,

the positive GND is only used in the 28V DC voltage domain - don`t ask me why. This box has several voltage domains like 25V AC used for example in the credit unit , 110VAC for the TT motor and neon lamp, 6.3VAC and 400VDC used in the amp.
They are isolated from each other by the main transformer. (seperate windings for each voltage domain)

The mute relais coil (located in the amp) "belongs" to the 28V DC domain (positive GND) , all the other DC voltages in the amp. are derived from the 400V DC domain which is using negative GND.

Regards...Jürgen

Hi Jurgen

thats cleared up my problem with the polarity of the caps, thanks, i realise now that the mute circiut in the amp is independent and has no connection to grd in the amp, got it!! at last am i right ? i meant to ask there is a dual 50 / 50uf 50v cap n the amp this is a paper type so i am going to replace it with 2 new these would have to be 47uf or 63uf 63v so am i better with lower or higher value ? your advice



cheers

mick



2 mal bearbeitet. Zuletzt am 03.07.19 22:20.

Hello Mick,

if the two grounds are connected isn't relevant for the polarity of the caps. In the 28V domain, the ground will remain positive, in the 400V domain the gnd is negative - see Marc`s example of the (+/-)40V supply in push-pull amplifiers.
The ground concept is one of the difficult tasks in electronic design as it affects hum and noise immunity. In my 1484, the schematic shows that the two grounds are connected at the amp. I think the idea was to run the wire for the cancel switch through the same harness and connector together with the signals for the volume control. In the box however, this wire does not exist and there are two separate wires running from the cancel switch to the mute connector outside the amplifier. I never measured it, but I assume the ground connection has been removed for good reason. This maybe different on your box. Sometimes schematics are wrong and the only way to find out is making own measurements.

Replacing the 2x50uF cap: If the amp. sounds well without distortions, there is no need to replace this cap. If all other caps. are old as well, you may want to consider giving the amp. to an expert.

Regards..Jürgen

Hi Juregen

i don't think there is much difference betwee your 1484 and my 430 the cancel switch and volume are seperate cables with the 3 pin connector on the mute cable. On my spare amp most caps have been replaced and there is slight distortion on the guitar parts of the record i thought it could be caused by a weak cap.There is not many experts around my area.
i would like to have one re-built, or do you know anyone selling a good amp 41710-a / 34725-a or someone to do a re-build let me know



cheers

mick

Hello Mick,
you can try a search here in the marketplace. If you can't find anybody to help out, you can give it a chance and replace the dual 50u cap. In my amp, one of the problems was indeed this cap. (1side dead). 2x47u is ok as a replacement. Of course, worn out tubes can also cause distortion. That`s about all you can do without having a sound electronic knowledge.
Good luck … Jürgen

Hi Jurgen

i have parcled up the amp a courier is collecting it on tuesday and it's going to a guy to be tested and checked so hopefully i will get some results in a few weeks ,so i will post when i hear news

regards
mick