5998A SET

[soundbrigade]

I heard today on the radio that some US company has made produced a GM salmon. It will scope up the oil in the gulf process it and shit it out together with the salmon itself i cans: Salmon filets in oil.

My stereo bench is braking down ...PHOTO!!!
The drawer on top got loose and so did most everything else and I had to glue the shit together.



The drawer. I will install it at the bottom of my shelf to minimize risks of a long fall.

[soundbrigade]

Never gotten my ass off the wagon to fix the was-working 5998A-SE. However when I start faultfinding, or more propably rebuild it, I want to use another driver than the 12AT7. How about 6SL7?

I also have to finish the 5998A-PSE ....

[EWBrown]

6SL7 should also be good, for driving the 5998.

With your indicated B+ voltages, try RK = 1K, RA= 100K, that should work out well.

/ed B

[EWBrown]

I've dug this one out of the burial crypt, again

I'm looking at 12AT7 / ECC81 SRPP driving PSET 5998As, B+ around 310-320 VDC, and using One Electron UBT-1 OPTs
(1600 ohms primary, 4/8/16 ohms secondary, 160 mA maximum Primary Current). I figure that the SRPP 12AT7s (whih I have used in
other SE designs, 6AV5GA and iothers) will have the necessary "oomph" to drive the paralleled 5998A triode sections, the single half a 12AT7
may fall just a bit short, otherwise.

I've re-entered the amp-building season, in the past couple months, I'vebuilt up a Budgie SE, a homebrew small-chassis form factor RH84 design (actually an RH89,
as the power tubes are UOS 7198As I pulled from a somewhat beat-up Fisher SA100 stereo amp), a second 6T9 SEP amp, and then re-built the first 6T9'er
that I built a few years ago, replaced a cheap intermittent step attenuator/volume control, and re-designed the power supply from the rather whimpy original
"Spare Time Gizmos" design, which was woefully under-powered. Now it sounds pretty good, before the upgrades, it sounded like a cheap 5-tube AC/DC table radio, at best, just in stereo ...
The 2nd one has GXSE10-8-5K OPTs which are an improvement over the original unit cheap 5K OPTs, and the power supply is vastly over powered, it can deliver 250VDC B+ at 220 mA, and I'm using about 75 mA total. No power-supply voltage drooping, now.

Also gutted out two somewhat beat-up and musty, dusty and crusty looking Dynaco ST-35 carcasses, these had seen 40 miles of bad road, the PC boards were crispy critters, and the original builder(s) must have been drinking cheap "plonk" wine or smoking funny smelling cigarettes, from the looks of the "craftsmanship", alnd one had been rather seriously hacked up - I wouldn't dignify it as being modified. I removed the iron, it checks out OK, though the PA774s are the early 1960s tar-dipped ugly version, and all of the trannies have the classic cloth-insulated leads, although cut fairly short, as per the ST-35 assembly instructions. These will definitely be "reincarnated" into future builds. The iron is 1963 and 1965 vintage.

So, after all of that, it's time for me to try something completely new and different , and the PSET 5998A looks like a good one for me to try! And, I have all the parts needed to make it so

/ed B in NC

[soundbrigade]

I will propably have some involontary vacation a little later so I should have time to get my SE-verson operating again and finish my PSE-5998A.

I am also interesting to hera from your project.

[Geek]

I will propably have some involontary vacation a little later...

[soundbrigade]

Our boss has to cut us loose for a few months in order to be able to increase the dividens from his shares in the company ....

[EWBrown]

The one thing that I would do differently from the original 5998A PSET, is to use separate cathode resistors and bypass caps for each triode section, and 1K grid stoppers for each, the combined transconductance will be very high, and the added resistors should prevent the likelihood of unwanted RF oscillation, and instability.

Sorry to hear about your involuntary vacation, I hope that you do get to return to the job, and meanwhile, make the best of a bad situation, build, build, build

Meanwhile, New Years' Eve is coming, plenty of smoked eels, lutefisk and "bread wine" for all

/edB in NC

[20to20]

The one thing that I would do differently from the original 5998A PSET, is to use separate cathode resistors and bypass caps for each triode section, and 1K grid stoppers for each, the combined transconductance will be very high, and the added resistors should prevent the likelihood of unwanted RF oscillation, and instability.

/edB in NC

Ed,

How do you choose the OPT Z value for these? Is Rp times a rule of thumb all one needs? Would Vp need to be considered? Skimpy data on this one.

[soundbrigade]

Awaiting an octett of 6SN7 (Russian origin) to go with a pair of bulke SE-trannies. Maybe next project after the 5998A an 6AQ5-SEs.

This is maybe off topic but here's a pic of our Swedish-Chicagoan Christmas supper. Eel - yes (upper left), no log-fish.

[20to20]

Awaiting an octett of 6SN7 (Russian origin) to go with a pair of bulke SE-trannies. Maybe next project after the 5998A an 6AQ5-SEs.

This is maybe off topic but here's a pic of our Swedish-Chicagoan Christmas supper. Eel - yes (upper left), no log-fish.

Magnus, for the Eel dish to be truly Chicagoan, you'd have to drop them in a big pot of Campbell's Pork & Beans. Beans and Weenies (with a backbone)

20 Happy Holidays!

[EWBrown]

I'd "wing it" for the OPT primary impedance of approx 5X the nominalinternal plate sresistance, given the operating voltage and current.. It isn't an exact science - 3X will gove greater output power, but at the cost of increased 2HD and 3HD. I find 5Xplate resistance as a good compromise. For a single 5998A triode section, 2.5 to 3K would be good, for paralleled sections, 1.25 to 1.6K should be a good match. I'll do up a "breadboard" with octal relay sockets first, and use the Heathkit variable power supply for the B+, before committing it to a permanent final project. That gives memore freedom to experiment during development.

The 5998A's Maximum PD rating is 15W per section, but that also takes in consideration having forced air cooling, I'd tone it down to 12 W per section, maximum, just to keep the tubes alive fr a longer time than running them at the full 30 watts total for both sections, those would run HOT HOT HOT

Lwt's see if this gets through this time, my last reply attempt got "SQL'ed" into oblivion by that demonic "General Error" problem

/ed B