• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

aikido heater voltage

Status
Not open for further replies.
Jump to Latest
E

evanc

Member
Joined 2009
#1
I recently built the aikido 9 pin all in one kit.
Aikido 9-Pin All in One Kit
I used 6CG7 tubes. The transformer heater output is 6.3vac. I have one thing that I need some help on. With the tubes out I get 6.3vdc at the heaters as I should. But with the tubes installed the heater voltage drops to 5.5v. The heaters are referenced to 1/4B+. B+ is just over 300v and the heater reference is at 73v. I have been listening like this and the preamp seems to work fine. I just wasn't sure if I needed to address something.
Thanks, Evan
 
#2
As long as the transformer doesn't run too hot (you're obviously running it at a higher load than it is intended for), you should be ok. Heater voltage is a bit on the low side, but as long as overall performance is as desired, there should be nothing to worry about.
 
#3
mastodon said:
As long as the transformer doesn't run too hot (you're obviously running it at a higher load than it is intended for), you should be ok. Heater voltage is a bit on the low side, but as long as overall performance is as desired, there should be nothing to worry about.
Click to expand...

Hoping I'm not hijacking this thread, but what if the opposite was true. What if the filament winding was underloaded and the heater voltage was more like 7 Vrms? I know a simple resistor in series can be used to drop the 0.7 V, but is it necessary? Would the higher voltage shorten the tubes life? Thanks.
 
#4
It'll work ok with +/- 5% heater voltage, but once you get too far beyond that it won't be optimal. Also, it looks like that's a regulated heater supply on that board, It's likely its dropping out of regulation at low voltage. You might have better luck configuring as a voltage doubler for 12.6 volts, if the board has that option.
 
#6
Whoa whoa. All you have is an Aikido preamp and it is dragging 8 amps worth of 6.3V down to 5.5V? Somethings not right. What is the primary rating? How sure are you that the secondaries are 6.3V and identical? I would double check that for sure. Could be that 1 winding is actually 5V or that the windings are indeed 6.3V but different VA rating.
 
#9
evanc: Not exactly what I meant... some Aikido boards have jumpers to put 6.3v heaters in series for use with 12.6v supply. What are the specs of the transformer you are using? By the way, I had a similar issue with my build when using 6.3v heaters, the reason 12.6 is easier is there is a smaller fraction of 12.6 lost to diode drop than 6.3, IIRC.
 
#10
Oh I see, 2 windings. It would be worth a try to put them in series for 12.6v. Leadbelly may be right though, maybe something's wrong there. Double check the heater regulator circuit, especially the voltage setting resistor on the reg.
 
#12
Good luck, let us know how it works out. If you change to 12.6 volts into the board, you'll need to make 2 changes (if that wasn't clear): change the resistor on the heater regulator section and also change jumpers on the audio section. Oh yeah, another reason why 12.6v DC is easier to get, is the regulator dropout is a lower fraction of the final voltage.
 
#13
Now, even setting up as a voltage doubler, he still MAY not be able to get REGULATED 12.6V to wire everything in series.

I would set it up as a voltage doubler to send ~12.6 to the regulator and then calculate the resistor value to get REGULATED 6.3V out. Vo=Vref(1+R2/R1)

Vo=1.25(typ)*(1+R2/120(TYP))

An R1 of 120 and an R2 of 480 should get you a nice 6.3 regulated.

An R2 of 1090 will get you ~12.6V if you wanted to try wiring the heaters in series. Might be worth a try.
 
#17
woodturner-fran said:
Would your 2 windings be out of phase with each other - try reversing how you have them paralleled and see if the heaters come back up. Also what is your mains voltage?

Fran
Click to expand...

No, I just realized what the thread is about, I misunderstood as well. The Aikido all in one has on board regulators to provide 6.3VDC. The 5.5VDC is perfectly reasonable; it is rectified 6.3VAC minus regulator dropout. Either live with it as 5.5 or rewire (as I think it is intended to be used) for 12.6 VAC input. Dropping rectified 12.6VAC (16.4VDC) to 6.3VDC is only about 24W load on the regulator, no problem with a decent heatsink.
 
#18
windings are in phase.

The regulator is on a good sized heat sink, but I don't have the experience to know how much power it can dissipate. If 5.5vdc is not causing a loss in performance or hurting the tubes then I am inclined to leave the circuit as it is.
 
#19
Ok, just got home... some measurements:

using glassware heater supply board powering 2 6cg7's (not 4)

line voltage: 126v ac
12.6v 1.2a rated transformer output: 13.7v ac
bridge output (low drop diodes) 15.4 v dc
regulator output: 12.9v dc

This agrees with the board docs,
Vac input 12 to 12.6 Vac for 12.6vdc output
for either full wave bridge or full wave center tap.

Doubler circuit spec'ed as requiring 6.3 to 8vac for 12.6 v out,
so yes, that might be closer to the lower edge.
 
Status
Not open for further replies.
Top Bottom