Does anyone know if they're detrimental to one's health if used in our devices?
Edit: I found that a smoke detector contains about 1 uCi of radioactive Americium (funny name!) while a 0B2 contains 0.0067 uCi. Apparently you get more radiation eating a banana.
http://large.stanford.edu/courses/2011/ph241/eason1/
Hello,
I tested my 26 preamp today, and sadly, it has some problems. With or without input signal, there is "motorboating" at the ouyput when connected to an amp. It does not matter what the attenuator setting (vol pot) is set to. I can hear the music, but masked by the dominant motorboating sound.
My preamp is a two chassis type connected via umbilical. One contains the PSU for B+, and the two filament regulators. The main preamp houses the HV Shunt Reg and the filament boards. The schematic is similar to this:
The pic below is the main preamp underside:
I measured the following
B+ supply to HV Shunt Reg=207
Vreg Out=150V
Shunt Current= 30mA (20mA for shunt reg and 5mA x 2 for the tubes)
Vrk(L channel)=9.35 V
Vrk(R ch.)= 10.3V
Vfil(pin 1-4) = 1.48V (Rchannel); 1.485V(Lchannel)
Vgrid L=0 VgridR=0
Coleman Supply voltage = 20.83V(R) and 21.86V(L)
Coleman Supply Out= 11.89V (L), and 10.88V(R)
I also have 390 ohms CC resistor for each channel as grid stoppers.
Can anyone tell me where can be the problem lies on this as I get loud motorboating sound on both channels.
regards,
Abe
I tested my 26 preamp today, and sadly, it has some problems. With or without input signal, there is "motorboating" at the ouyput when connected to an amp. It does not matter what the attenuator setting (vol pot) is set to. I can hear the music, but masked by the dominant motorboating sound.
My preamp is a two chassis type connected via umbilical. One contains the PSU for B+, and the two filament regulators. The main preamp houses the HV Shunt Reg and the filament boards. The schematic is similar to this:
An externally hosted image should be here but it was not working when we last tested it.
The pic below is the main preamp underside:
An externally hosted image should be here but it was not working when we last tested it.
I measured the following
B+ supply to HV Shunt Reg=207
Vreg Out=150V
Shunt Current= 30mA (20mA for shunt reg and 5mA x 2 for the tubes)
Vrk(L channel)=9.35 V
Vrk(R ch.)= 10.3V
Vfil(pin 1-4) = 1.48V (Rchannel); 1.485V(Lchannel)
Vgrid L=0 VgridR=0
Coleman Supply voltage = 20.83V(R) and 21.86V(L)
Coleman Supply Out= 11.89V (L), and 10.88V(R)
I also have 390 ohms CC resistor for each channel as grid stoppers.
Can anyone tell me where can be the problem lies on this as I get loud motorboating sound on both channels.
regards,
Abe
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Hello Regal,
I am using K&K HV shunt reg. I set the current to 30 mA and regulated voltage to 150V from 207Vdc input to have 145V on the plate. The example in the documentation had 300V in and 250V out at 40 mA(20mA for the reg and 20 mA to the tube circuit as an example).
How do I check if its oscillating?
Abe
Definitely not. The K&K Salas regulator is good to 1000VDC input.
Motorboating is often caused by a bad PS cap or a bad ground in the PS circuit. Check there first.
You would need a scope to check for oscillations. Even with the K&K shunt you are dissipating a lot of wattage, can you adjust the output voltage to see if it is working, also check the shunt milliamperage?
The other thing is the choke input supply, these can be troublesome.
If the motorboating is of low enough frequency you can use 10 ohm resistors in series before and after the shunt and check for AC with a multimeter.
I would also double check grounding, with my dual case build I put the star ground in the power supply chassis, I vaguely remember having motorboating and it was a scatterbrain grounding mistake.
Hi Abe,
Please make sure that the last B+ cap (C2 in the schematic) is located in the Signal-chassis. It should be mounted near to the CCS-input for the Shunt Regulator.
In the same way, if the supply cables to the fillament Regulators are long, a 1000uF 35V Panasonic FC or similar (low impedance) cap should be used at the input of the regulator PCBs.
And to answer an earlier question: the input-output voltage of the filament regulators is too high.... 5V is ideal, there is little to be gained from increasing above 5V, and the transistor Q5 will get hot above this. If you have raw dc-to-output difference of 10V, this must be reduced, to 5-7V.
As others have mentioned, please check that Ground-Central is on the signal chassis, near the input socket.
Please make sure that the last B+ cap (C2 in the schematic) is located in the Signal-chassis. It should be mounted near to the CCS-input for the Shunt Regulator.
In the same way, if the supply cables to the fillament Regulators are long, a 1000uF 35V Panasonic FC or similar (low impedance) cap should be used at the input of the regulator PCBs.
And to answer an earlier question: the input-output voltage of the filament regulators is too high.... 5V is ideal, there is little to be gained from increasing above 5V, and the transistor Q5 will get hot above this. If you have raw dc-to-output difference of 10V, this must be reduced, to 5-7V.
As others have mentioned, please check that Ground-Central is on the signal chassis, near the input socket.
Hello Rod,
First off, the motor-boating I am hearing about is a high pitch sound. It is present as soon as the preamp is ON.
I have the "Ground Central" as per your advice, at the input of the tube circuit( between the two sockets in the the pic above) where IEC, 0V and negative filament(bottom of the cathode resistors) terminates to as well as all the shield of the cables and chassis connection. One single point for all of them.
I will take a pic tomorrow. Right now it is too late and I've checked the grounding of the PSU chassis and main preamp chassis.
For the PSU B+:
HV taken from AZ1 filament --->20H --->47uF(center tap of HV connects here at the bottom)---> 10H ---> 47uF --->0.36H ---> umbilical to main chassis ---->K&K HVShunt reg ---->LL1660 ---->plate
For Filament(Rod Coleman Regs) each:
Bridge --->440uF ---->60mH --->30000uF ---> umbilical --->Rod Coleman regs ---pin4 --->pin 1 ---->10 ohms ----> filament reg "minus" ---->ground central.
K&K Shunt reg easily adjust current (20mA + circuit requirement) and voltage(regulated at about 150V right now).
I cannot figure out why there's always a high pitch sound as soon as the preamp turns ON and it is very loud!
I will check the circuit out again tomorrow. It's about 2AM here now.
regards,
Abe
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Hello Abe, I think the quickest item to try is B+ regulator stability. Please add some HV capacitance located near the input circuit of the B+ CCS/Shunt regulator. 22uF or more for preference, but even 10uF may be enough to stabilise it.
Before using the amp for a long period, the input-output voltage difference for the filament regulators (10V as indicated) must be reduced to 5 .. 7V, or the transistors may suffer from overheating.
Before using the amp for a long period, the input-output voltage difference for the filament regulators (10V as indicated) must be reduced to 5 .. 7V, or the transistors may suffer from overheating.
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We are talking about the resistance of the HV winding of the power transformer secondary connected to the plates of the AZ1 right?
Abe
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I will do this tomorrow. It is almost 3AM here. I gotta go, thanks and I will continue later...
Abe