ODS with Deluxe Txers - 2x6V6 Problem

[danotron]

I built a ODS similar to a 102 but I used Hammond Deluxe Reverb output and power transformers. I used the 5v winding for relay and indicator light.

There is around 450 on the 6v6 plates and I am using JJ's. The other tubes voltages are a little higher then normal but the amp sound great. It is extremely loud....seems louder then it should be. The bias is around 18mA.

When I really crank up the amp my indicator light will dim and the amp starts to fart out...like it PT can't keep up. The relay power will also crap out and the relay will switch.

Has anyone had a problem like this before? Any suggestion on how to fix it? Should I drop some voltage with a power resistor on the main centre tap?

[talbany]

Has anyone had a problem like this before? Any suggestion on how to fix it? Should I drop some voltage with a power resistor on the main centre tap?

Your problem is not voltage it's current!!

Do the mA math on the tranny (or post the specs of the power transformer here and others can help)..If the specs jive then you could have something in the amp drawing too much current perhaps a bad filter cap or even a bad PT..Also does the power transformer get real hot?..
Hammonds are generally good transformers with good quality control!

I built a ODS similar to a 102 but I used Hammond Deluxe Reverb output and power transformers.

On a different note.. It's not a Deluxe PT if it's running @ 450?

Tony

[PaisleyTube]

Loud is good

50 or 100 Watts ain't that much louder than 20-25 Watts IRL.....

Lower volume:
- lower eff. speakers
- tweak the circuit so it will sound better at lower volume-settings (did I say that regarding a Dumble? Yes, I did say that ha ha)

[PaisleyTube]

without a GZ34 rectifier tube the voltage will be higher when using a DR PT.

check every solderjoint in the powersupply

[danotron]

I did some measuring here's what I get.

6v6 plates = 448V
PI = 290v
V2a = 194v
V2b = 200v
V1a = 193v
V1b = 197v

PT = Hammond 290BX 330-0-330 138mA, 6.3v 3A, 5v 3A

Could 138mA be to light for this cct? The PT does not get hot at all.

When I run it clean and cranked there's no problem. This only happens when the OD is kicked in.

[talbany]

I did some measuring here's what I get.

6v6 plates = 448V
PI = 290v
V2a = 194v
V2b = 200v
V1a = 193v
V1b = 197v

PT = Hammond 290BX 330-0-330 138mA, 6.3v 3A, 5v 3A

Could 138mA be to light for this cct? The PT does not get hot at all.

When I run it clean and cranked there's no problem. This only happens when the OD is kicked in.

Well this makes no real sense to me..
Unless your getting some high frequency oscillation and causing your tubes to run away.I would also double check your relay supply wiring .Also replace V2 tube while your at it..Voltages look close enough
An accurate diagnosis on an internet forum!!

Good Luck!!

Tony

[M Fowler]

Did you regulate that 5v supply with a 7805?

[danotron]

I did use a 7805 but its 5.6v before it and 4.3v after ...I think the problem may be that a full power the voltage is dipping and turning on and off the relay.

Is there a good fix for this?

[ToneMerc]

The 780x needs to see at least 2-3V above it target output, beyond that any additional voltage is wasted and is dissipated as heat. Your input is right at the target voltage. Seems odd as you should have at least 7V I would think. Normally, the relay AC is 6.3V in doubler or bridge configs. Brownnote ran the relays unregulated from the 5V tap, but you can run into problems with several relays and LEDS.

What relays are you using? Are they the low current Omron?


1. Bypass the 7805 and attempt to run the relays from the bridge only. This still might be tricky if you have FTSW LEDS and the indicator LED to power as well. I believe the H2-5V Omron min. coil voltage is around 3.2V, IIRC.

2. It appears you need any additional current, remove the "On" indicator from the relay supply and power it from the filament string like HAD.

3. Install a small 6.3 PT for the relay supply.

4. You could reconfig the relay supply as a doubler and use 12V relays, but then you have the piggybacked indicator to deal with.

I personally think the PT is a tad light on the HT winding for this style of amp. Nevertheless, what you are experiencing should not be this extreme. However, using at least Vibrolux iron such as the 290CX would have given you greater flexibility in the long run.

TM

[talbany]

What does not make sense..

If the PT was/is being Taxed or bad it would be getting hot..It's Not!!
Why is the amp farting out (whatever that means) in OD. but sound great in clean...Could have nothing to do with the Xformer..Dont know??
If it were a relay supply issue why does do it on OD relay and not the PAB relay boost (same current draw)..Or does it?..What are the relay voltages with the transformer under load?...Don't know..
Also why does it do it only when he play's the amp and not at idle on a seperate supply winding that draws very little current on a transformer that doesn't get hot..Could be a vibration issue..Does it do it with the amp isolated?..Don't know
Also what is the line voltage at..Don't know?
Also do you have the footswitch attached or does it do it from the toggles on the front and or back..Don't know?..Could be your footswitch is the problem?

These are just a couple things off the top of my head .I am sure if the amp were on my bench there would be a few more..

Good Luck

Tony

[wjdunham]

With the 25W amps there's a fine line in balancing the low end to keep the amp tight and shaving off too much so that it sounds thin. The Deluxe output transformer is not that big and will cause some ugly distortion when pushed too hard. I'd suggest putting a 50W zener in the center tap of the power supply secondaries to drop the plate voltage down around 400V to keep from stressing the 6V6 tubes too much above their spec.

Then try lowering the cathode bypass caps on the OD down to 1uf. Make a few small tweaks and test out before moving to the next tweak, there are a few other places to tame the lows, but I've found it doesn't take much and the 1uF cathodes was a good compromise.

Bill

www.sebagosound.com

[tictac]

The JJ 6V6's should be able to handle 450V fine (according to their spec sheet) seems like your interpreting the indicator lamp reaction as something it probably isn't.....

The afore mentioned bypassing the Vreg, wiring the lamp AC seems like the right thing to do at this point.

If you're PT is happy and your power tubes aren't redplating sounds like your amp is working the way it should....

TT

[danotron]

When I bypassed the 5v regulator the problem stopped. To confirm I took the bypass off and the problem started again.

I am only running one relay and two LED (power and channel indicators) from the 5v winding.

I can now work on a solution.


Thanks everyone for your help!

[amplifiednation]

Let's see some pictures!

[tictac]

Sounds like you need to separate the lamp and relay circuits. A small Rat-Shack 12V PT is an easy install and would allow you to operate the 5V regulator for the relays and use the 5V PT winding for the lamp.

TT