828 is better

[danFrank]

rdf said: The 828 is better.

Hello,
Could you share you experiences with this tube? Like plate voltage , G2, G3 voltage, load worked into?
The RCA data sheet says it performs very well as an audio tube with very little distortion. I always wanted to make a high power amp with these or the 813. I now have the OPT which will work well with either of these.
Thanks, Daniel

[cotdt]

better than what?

[danFrank]

Than the 814. This was in the 8-807 post but thought I'd start another post as it was getting off topic.
Basically looking for anybody's personal experience with the 828 tube.
Daniel

[Miles Prower]

These types: 814 and 828 are both 807-oids. The design comes from around the same time, and use the same design philosophy. The intent was to design a highly efficient RF final by keeping both DC screen current and voltage down since screen power doesn't contribute to output power. It so happens that this same design makes for some mighty fine, low distortion, audio finals.

The main difference is in power handling, and voltage limits. The 828 has a higher plate dissipation rating than does the 814, and can take significantly higher voltages. Class AB1 828's can do nearly 400W of audio output. Sure, if you need it, then why not go for it?

If you need somewhat less power, depending on your requirements, then either the 814 or 807 are excellent choices.

In any case, a pair of 828s sure beats heck out of paralleling a whole bunch of 807s with the subsequent added complexity of needing a fancy bias circuit to keep 'em all pulling together. Also, be a helluvalot easier to drive.

[rdf]

Hi Daniel, that comment was made in the context of rcavictim's about triode SE. The 828's great advantage, depending on which data sheet you believe, is almost double the screen voltage limit of an 814. I was/am also looking a suitable use for my Hammond 1628SE OPTs, their debilitating flaw when used 5k:8 ohms almost disappears used 10k:8 off the 4 ohm tap. This tranny has more than enough iron to handle the connect.

In that context, a fixed bias, triode connected 828 running max screen voltage of 750 V (about 800 Vp, 825 B+ with the Hammond's high DCR), into a 10k:8 transformer, made around 13 watts RMS at 0.6% predominantly 2nd followed closely by 3rd, anything above falling off rapidly. Third dropped rapidly with level, 2nd dropped much more slowly and was in the 0.3% range at 1 watt, very much the dominant harmonic. I'm sorry I don't recall the exact grid bias but it was in the range of 95-100 volts, standing current around 80 ma. The tube was running around 60 watt plate dissipation. The driver contributed a little 2nd harmonic cancellation but not much, I would guess in the 25% range. Damping factor was around 4.

The circuit is still on the test 'plank' but I've moved on to clearing a couple other projects. The limited auditioning during testing with a Jordan full range was very, very promising. It's one I'll return to. Since I have a second set of defective OPTs - single-ended SE toroids someone forgot to gap - I'm also wondering what kind of paraphase pentode cathode followers those 814 make.

[Tweeker]

You could try an SRPP for the defect toroid OPTs, they could be well suited for that.

[Dave Cigna]

Originally posted by Miles Prower
These types: 814 and 828 are both 807-oids. The design comes from around the same time, and use the same design philosophy.

It's tempting to think that. The 828 seems to fall neatly in between the 807 and 813 (I know nothing about the 814.) But I can say with certainty that the 828 and 807 share little in terms of construction. Besides the obvious directly heated thoriated tungsten filament, the 828 does not have beam forming plates and aligned grids. It does have a true suppressor grid. There are boxy 'beam plates' at each end of the plate structure, which I suppose is why RCA calls it a beam tube, but it is not a beam tube in the same sense as a 6L6 or 807.

I'm not suggesting that these features make it necessarily good or bad, just that I would call it a baby 813 more than a jumbo 807.

[kstlfido]

Stumbled across this thread while looking for 828 tube info. I just got a pair to play with. Could anyone that tried this tube share their experience?

I was looking at the 828 specs and noticed the typical operating characteristics show the suppessor operated at around 60 volts positive to the cathode. I would usually connect suppressor grid to ground. Any comments?

This does look like a good tube for my amp project for Burning Man. I will try UL and fixed screen and see what I get.

-Kent

[tubelab.com]

The 828's great advantage, depending on which data sheet you believe, is almost double the screen voltage limit of an 814. I was/am also looking a suitable use for my Hammond 1628SE OPTs, their debilitating flaw when used 5k:8 ohms almost disappears used 10k:8 off the 4 ohm tap.

HMMM, I have a pair of 1628SE's and a box full of 828's maybe the two should meet.

I was looking at the 828 specs and noticed the typical operating characteristics show the suppessor operated at around 60 volts positive to the cathode. I would usually connect suppressor grid to ground. Any comments?

This was a common trick to cure oscillation that ocurrs when the tube goes into or comes out of cutoff. It may or may not be needed depending on the particular tubes and the circuit layout. G1 and G2 (and maybe plate) stoppers should be sufficient.

[kstlfido]

Thanks George. I will be breadboarding them out in the next few days.