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 866jr B+ delay and delay relays

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RadioShack



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Join date : 2010-10-18

PostSubject: 866jr B+ delay and delay relays   Mon Oct 18, 2010 6:23 pm

I know it it good to delay the b+ to mercury tubes
Q1: does it have to be delayed?
Q2: Would edison delay relay tubes work? I have 4, 2 with 6.3 volt (heater) 60 sec delay contacts:150vdc 250ac 3A, and 2 117v (heater) 75 sec, contact:150vdc/250vac 3A
these will be switching 375vac
Q3 Mercury tubes cant handle large input capacitors, If I place a large (10hny) choke from the filament to a 40mfd cap can the tube handle that?

This is going to an audio amp, not a transmitter.

Thanks for any help,
Ian

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radiotechnician



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PostSubject: Re: 866jr B+ delay and delay relays   Tue Oct 19, 2010 1:26 am

You must delay the AC supply to the plate while it the filamant warms up. The timer should be connectect in the plate supply transformer primary. Forget trying to relay the AC highvoltage
lead to the plates that's just asking for grief. This means you need two transformers-filament and plate voltage.

Could you post the schematic of the audio amplifier you are going to build?


de

VE7ASO.
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Alan Douglas



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PostSubject: Re: 866jr B+ delay and delay relays   Tue Oct 19, 2010 10:22 am

It's customary to use the thermal-delay relay to operate a larger relay, since the contacts are slow to open and will arc. They definitely won't switch 375VAC.

Without looking up the exact details, if you apply AC to a mercury rectifier without sufficient mercury vapor, it acts as an ordinary thermionic rectifier and the cathode will be destroyed by ionic bombardment. With mercury present, the maximum anode potential is limited to about 13 Volts which also limits the ion energies. Or something like that. You can get away with it in low-power applications (1933 radios) or in Hickok tube testers where there's no current flowing until the Gm button is pressed.

Answer to Q3 is yes, assuming a full-wave rectifier (you can't use a choke with a half-wave rectifier). There may be limits on the choke size, and it may be preferable to use a small input capacitor ahead of it. I'm not up on transmitter power supply design.
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Gary Kaufman



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PostSubject: Re: 866jr B+ delay and delay relays   Tue Oct 19, 2010 8:38 pm

I've worked quite a bit with 866jr's and they are a frustrating tube.

Despite their ratings, for any B+ over 600vdc you'll have to hand select them.

I pre-heat the filaments on the 866jr's for 2-4 minutes depending on room temperature with a time delay. I have them choke loaded in a LCLC design with both swing and smoothing chokes. I have an additional damper diode before the first choke. I apply both B+ and filament to the damper diode at the same time. The very slow turn on of the damper diode allows a "slow start" to the B+ and prevents flash over.

If this isn't clear I could probably draw up a circuit.

- Gary
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RadioShack



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 12:05 am






The first image is what is there, the second is my plan.
I AM NOT MODIFIYING THE AMP the 866jrs',relay and choke are on a seperate chassis. essentially I am subbing them for a 5u4.
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Jon the Grimm

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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 5:45 am

Remember, with a choke input filter, the output volts are no more than approximately .9 times the AC rms voltage. As drawn with that power transformer and 220R resistor, B+ would be about 280 volts.

It is also better to use a 2.5v ct filament transformer and take the rectified ac from the ct in order to reduce hum. It might be a good idea to add a thermistor to the plate transformer primary to make the B+ come on slowly. Also bleeder resistors are generally employed in choke input filters.

Oh and one more thing: all the other tubes in the amp need to be preheated at the same time as the rectifiers in order that they be ready to conduct as the B+ comes on. Otherwise there will be a initial voltage surge which may blow up the filter capacitors.
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RadioShack



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 10:00 am

can I switch the b-? centertap to nothing untill relay shorts it to ground?
What resistance should the resistor be to mimic the voltage drop of a 5u4?
Ian
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dkjones96



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 10:18 am

I did this same thing in a 6V6 amplifier(well, i used 816s bust still) and have a main switch for the power transformers and a center tap interrupt switch.
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radiotechnician



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 11:21 am

Get a seperate filament tranformer for all the tubes in the amp except the 866JR.

Connect the heater of the time delay relay to the same filament circuit as all the amp tubes.
Use the contact in the TDR to switch on the old transformer primary (now used as only the transformer
for the B+ rectifier) Make sure it is rated for < 3 amps 120 VAC.


I would be interested in learning if the 866JRs and your choke somehow caused a new buzz which got coupled back the 6267 (EF86).


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dkjones96



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 12:39 pm

It should be noted that series filaments aren't recommended over 300ma...

You need a transformer for parallel operation or you can attach the center tap between the tubes instead of just having it for ground.

http://www.guitarpartssite.com/HAMMOND-P-T166S2-p/p-t166s2-ce.htm
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RadioShack



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 12:55 pm

I have a kolster k-44 power amp. It uses 2 (81) tubes for the rectifiers. They have series filaments attached to a 15v winding. They have about 375 volts on the plates. It works fine.
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dkjones96



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 1:09 pm

Never said you couldn't, just isn't recommended.

1.25 amps will also balance easier between the two heaters than 5 amps will. As current demand increases the harder it is to keep the two tubes within specs while in series operation, especially during warm-up.

But, like i said, a simple end all be all for you is to just connect the center tap to the bridge between the two tubes. Then you've got 2.5 across each one and it won't matter if the heaters don't match. That's what I did with my dual 6CA4 setup. The transformer for those is 12.6vct and the center tap goes between the tubes.
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Jon the Grimm

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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 1:55 pm

The current power transformer is completely unsuitable for a choke input filter. Here's why:

With a capacitor input filter, the maximum theoretical dc voltage available at the output is equal to the peak ac voltage from the transformer. Peak ac is approximately equal to 1,4 times the rms voltage. This does not include losses from the rectifiers' impedance or the resistance of the filter.
With the original transformer and a c-input filter, 1.4*375=525 is the max voltage you could get if their was no resistance in the rectifier and filter circuit. Plenty of volts are left for B+.

However, with a choke input filter. the maximum dc voltage available at the output is approximately equal to the .9 times the rms voltage from the transformer. This also does not include losses from the rectifiers' impedance or the resistance of the filter.
With the original transformer and a choke input filter, .9*375=337.5 is the most you could get. Subtract 15v for the rectifier voltage drop and another 25v for the choke's resistance and your down to under 300v.

In order to get the correct B+, you would need more like a 525-0-525 transformer.


The filaments on these big MV tubes may draw significantly different current from each other. In series this could decrease tube life or cause an imbalance which could greatly increase noise. Tube manuals specify that the B+ be taken from the center tap of the filament transformer for mercury vapor tubes, also for balance reasons.
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RadioShack



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 2:36 pm

so is there any way to make this work?
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RadioShack



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PostSubject: Re: 866jr B+ delay and delay relays   Wed Oct 20, 2010 2:39 pm


also they are 866jrs 2.5v 2.5 amps no plate cap
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Gary Kaufman



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PostSubject: Re: 866jr B+ delay and delay relays   Thu Oct 21, 2010 3:32 pm

Please take this as a friendly comment, but I honestly think you're wasting your time.

I've worked extensively with 866jr's, here is a power supply for a 211 amp:



They really have nothing to offer to the Eico HF22/35 circuit.

If you want to build something from scratch the 866jr's are a pain, but could be fun - but why try and shoe-horn them into an existing (and well done) design?

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RadioShack



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PostSubject: Re: 866jr B+ delay and delay relays   Thu Oct 21, 2010 5:58 pm

I know I am wasting my time with this... I just wanted to experiment with them in the Hf22

I am building an amp from scratch however(later), I started some work but have since lost the schematic...While typing this I found it.... it will use 866jr tubes.

Did your amp use an input capacitor? If so what value?

Ian
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Gary Kaufman



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PostSubject: Re: 866jr B+ delay and delay relays   Thu Oct 21, 2010 7:45 pm

The supply in the picture provides 825vdc. It is "mostly" choke loaded using swing and smoothing chokes. There is a small 0.1uf cap before the swing choke to provide a reduction in "buzz" from the choke. It has only a minimal effect on B+, and the supply acts pretty much as a choke loaded supply.

Caps are minimal - a total of only 30uf. Chokes do most of the filtering.

Pick up some of the ARRL Radio Amateur Handbooks from the 60's. They have very well written tube rectifier based supply designs to study and learn from. Also download the very well done tube power supply designer software from www.duncanamps.com - it is a great tool and you can study the effects of changes to a design.

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