heybluez74
TDPRI Member
I am working today so won't be able to get to this till later but I am planning on triple checking all my connections/wiring just to make sure I did not make a dumb mistake... more soon
DIY 5F2A: Distortion, not loud. Where do I look?
- Thread starter heybluez74
- Start date
The transformer is rated for 600V @ 173mA, almost double the current usually used. Due to this there is less sag across the secondary winding causing the high voltage. Putting a 600R resistor in place of the 500R will cause less current but will also increase the voltage a little. So not the way to go. The heater voltage is 3.6 x 2 = 7.2V rather than the 6.3V. The winding is rated for 5A, you are drawing 1A.
heybluez74
TDPRI Member
So best to get a proper PT?
Will you be using the current transformer for another amp? If not and you do not want to spend the money you can reduce the voltage by putting resistors in series with the heaters, zener diodes for the supply voltage.
heybluez74
TDPRI Member
I don't plan on using it for another amp (even though despite my current frustrations, building this amp is a lot of fun). I think I get the series of resistors layout but any tips/links re: using zener diodes for supply voltage?
heybluez74
TDPRI Member
Curious -- when I look at the spec on the box of my Hammond 272FX it looks like it is rated for 600V 150m ADC, not 173mA. Where are you getting that from? (asking so I can learn)
Also, would I use the GRN/GRN-YEL to get 6.3V to the heater? Right now, using GRN-GRN.
dan40
Friend of Leo's
When we look up the specs on the Hammond website, I get the same results that Printer is quoting. It's odd that your box says something different. It's possible that Hammond made a design change recently and your is an older model.
Your heater voltage is high because the filament winding has a very high current rating. It was intended to run a lot more tubes, or tubes with a higher current draw. Since you are only using 1 amp instead of the 5 amps that it's rated for, the voltage will tend to be higher than normal.
You should have both green wires running to the pilot light and tube sockets and the green/yellow centertap wire connected to ground. If the green/yellow is not connected to ground, this could also be causing your hum.
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www.hammfg.com
The windings each have their own resistance. As you draw current there is a voltage drop across the resistance (V = I x R). To deliver 6.3V at the spec'ed current of 5A the open circuit voltage has to be above 6.3V. Just for kicks let us say it is 7.5V with no load and 6.3V at 5A. At 2.5A it would roughly be 6.9V. Tubes usually can operate +/- 10% of 6.3V although they would rather be within 5%. As said above, the GY should be at ground potential, or at a higher dc voltage such as the capacitor across the 6V6 cathode resistor. This is called an elevated heater potential. Try grounding the wire. After you sort out the amp's operation and you still have some hum you can try elevating the wire.
Can you take a picture of your input jack?
sorry Hey blues.
you did measure and show it.
however,
a 300-0-300 spec
and a 342 VAC measurement just don’t go togethor.
and
and
don’t go togethor either.
I recommend starting with the VAC the power transformer is putting out and go from there.
and
don’t go togethor either.
I recommend starting with the VAC the power transformer is putting out and go from there.
As fender amps go, 300-0-300 is low. (tweedish?)
the plate voltage is not too bad. The plate dissipation Is high and only too high for a tweed amp but not for a BF/SF champ which this amp is not.
he has
434 plate minus 24 cathode for 410 volts. High for tweed but not too high for a BF/SF champ.
the plate voltage is not too bad. The plate dissipation Is high and only too high for a tweed amp but not for a BF/SF champ which this amp is not.
he has
434 plate minus 24 cathode for 410 volts. High for tweed but not too high for a BF/SF champ.
your voltages, current and plate dissipation are all in range, although on the high side, especially for a tweed circuit.
being a little high will not cause
unless the tube is no good.
being a little high will not cause
unless the tube is no good.
heybluez74
TDPRI Member
heybluez74
TDPRI Member
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heybluez74
TDPRI Member
reversing the OT wires fixed the distortion and weakness. Now it is a hum/buzz.... also strange is that I can wave my hand over the preamp section (12AX7) and it will have an effect on the noise. Grounding issue?
heybluez74
TDPRI Member
Here is what it sounds like at this moment --
So def has power... just hum plus slight distortion... and what I would say slight chorus effect (even though I kind of dig it). Would you all still consider this a power supply issue?
So def has power... just hum plus slight distortion... and what I would say slight chorus effect (even though I kind of dig it). Would you all still consider this a power supply issue?
With the tube dissipating 19W how do you suggest cooling it down?
A power supply of 410V is already high for SE, 434V is more so.
thanks for clarifying.
688/2 = 344
344 * 1.414 = 486.4 VDC - 48.4 VDC = 438 VDC, the B+ voltage.
I calculate your 5Y3 drops 48 VDC. a little less than expected.
I agree with lower left coast.
I recently tested some 5Y3 tubes for voltage drop.
the chart says 60 volts. NOS tubes drop 80-90, old RCA tubes drop 110-120.
Hey Blues. The amp sounds good.
I would look for red plating in the dark and in the light.
if the red plating were minimal I would consider running the amp as is.
as lower left coast recommended, a rectifier tube change could help.
this seems viable to me. The AA964 Princeton schematic shows 420 VDC on the plates. The OP has some wiggle room.
a combination of both would work really well.
lower the voltage with a different rectifier tube and then lower the current with a rebias.
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