My new amp build - not singing the blues!?

[armillary]

Sorry, duplicate posting error.

[armillary]

Sorry, another duplicate posting error.

[funkgang49]

If you put the choke before the first filter cap you will get a very large drop in B+. If you put the choke between the first filter cap and the second filter cap you will get a very small drop in B+. It sounds like you have it before the first filter cap.

Choke is placed before 1st filter cap. The choke is a Hammond 158Q: 5H 150ma with a DC resistance of only 105 ohms.
Voltage measurement at choke side of standby switch is only 280v before it hits choke. After choke at 1st filter cap voltage rises to 292v?! It should drop only by a few volts, no? Continuing on after 3K dropping resistor at 2nd filter cap voltage drops to 277v.

With only 280v at standby switch it would imply that I must have a wiring issue somewhere, power supply, PT, OT?
I've checked all ground related solder points and grounding scheme. Everything looks okaly-dokaly.

Again, without a schematic and full specs on the transformers, there's not much to be offered in the way of help.

I have downloaded specs on PT & OT from MM that I'll try to post. Still fumbling with schematic in ExpressSCH.

Again, I like cooler biased tubes, but not that cool! Don't adjust your bias resistor until you fix the rest of the amp though.

Ditto Matt, that's why I used a 500 ohm. I definately won't adjust that resistor since that is not the source of my issue. I was expecting somewhere around 400v so I'm sure there is a wiring descrepancy somewhere. I was hoping to narrow it down while I complete the schematic.

[Jana]

Do you have a filter cap prior to the choke? What is the value? If I understand your description correctly, it sounds to me like you don't have a cap prior to the choke. This makes the power supply a "choke input" arrangement. While this provides much better regulation, it drops the voltage quite a bit.

[armillary]

"Voltage measurement at choke side of standby switch is only 280v before it hits choke. After choke at 1st filter cap voltage rises to 292v?! It should drop only by a few volts, no?"

No. You won't see the drop across the choke. Where your choke is currently placed it lowers the B+ output of the rectifier tube. It's opposing the ripple, not smoothing it like a capacitor.

[funkgang49]

If you put the choke before the first filter cap you will get a very large drop in B+. If you put the choke between the first filter cap and the second filter cap you will get a very small drop in B+. It sounds like you have it before the first filter cap.

Yes, the choke is before the first filter cap.

Where your choke is currently placed it lowers the B+ output of the rectifier tube. It's opposing the ripple, not smoothing it like a capacitor.

Gotcha. I'll place it between 1st and 2nd filter cap.

Should the voltage tap for the OT be placed at 1st filter cap or 2nd filter cap?

[Jana]

You can leave the tap for the OT transformer after the choke--in fact, with a SE amp, that is what I would recommend. But, you should have a filter cap prior to the choke if you want those voltages to be higher. Really, all you need to do is add one more cap.

[Firestorm]

What rectifier? If its a 5U4, those voltages don't seem far off for a choke input.

[armillary]

The OT red wire should go to the 2nd filter cap, based on SE amp schematics I've looked at or built. Champs and Princetons.

[matt h]

(deleted)

[armillary]

I would not use a tube rectifier in a single ended amp.

Respectfully, why?

Hey, I got Merlin's Preamp book (second edition) yesterday. I'm up to page 9! The RCA RTM rating charts are starting to make sense!

[matt h]

(deleted)

[funkgang49]

Placed choke between 1st filter & 2nd filter and put OT tap at 2nd filter... DISCO! Voltages are right on.

With JJ GZ34/5AR4 Recto & 6L6 Output:
Plate - 390v
Cath - 29v
Screen - 388v
OT tap - 382v

Thanks Jana, Armillary!

Why not a tube recto? Expense, in many ways. In no particular order:

- monetary cost
-"real estate" (cost in size/layout)
-heat
-wasted voltage

All excellent rational reasons for not using a tube recto...

"put in different tube rectos for different desired voltages!" becomes a thing.

At the time that I started this project I wanted to switch out different recto's; 5Y3, 5U4, GZ34 for different voltage drops which could probably be handled just as well with a VVR. I also have a plug-in Solid State rectifier I can pop in.

I have hooked up the MV with the input coming from the "In Phase" output of the LTPPI and have added a 1.5K grid stopper at the Power tube Grid.

2 Issues:
1. Turning up the MV 2/3rds or about 2 O'clock there is a loud wail or squeal with some noticeable hiss.
2. Headroom - I would like to raise the clean headroom. Currently I am using a 560 ohm bias resistor with a 10K tail resistor in the Phase Inverter.

I know, I know, Matt you're right - a schematic would make this all much easier.
Holiday weekend and I'm hosting! I'll try to get one up by Mon. evening.

Thanks everyone for all the help y'all are great! Happy Holidays!

[matt h]

(deleted)

[funkgang49]

as far as squealing with the MV goes, remind me if you used NFB (presence) loop? if so, it's possible it's backwards.

I have a 100k resistor from top of 10K "tail resistor" back to tip of speaker jack.

As far as clean headroom goes, uh, "use solid state recto as your starting point", that'll net you higher voltages. Remember that "plate-to-cathode" voltage are what your tubes care about. So by increasing the bias resistor, creating more cathode voltage, you're also shrinking headroom.

I was under the impression that as you go up in cathode resistance, i.e.; 400 up to 500 ohms that the tube is biased colder and hence more headroom - so if I understand you correctly I should be going down from 500 ohms to say 430, 400, 360 ohms to achieve higher clean headroom?