tube fanatic

http://www.radioera.com/radioera.root/shop/ If they can't help you, I'm sure they know of folks who can.

The big question you need to ask yourself is if it's worth the trouble to properly set up such a system. Years ago a friend ran triamped with a custom bass bin for both channels each containing a pair of 15" Altec woofers (the bins were the size of refrigerators); those crossed over to Magnepans (I don't remember which ones offhand) which then crossed over to Janszen electrostatic tweeters. It took him a year (literally) to get the equalization just right. He ran full SS amplification with a total power per channel of a couple of kilowatts. Admittedly, the result was quite something to hear. The cannons in the Telarc recording of the 1812 overture made me feel as if I got kicked in the chest by a mule (almost as much fun as street racing in another friend's 1970 Z28 which turned the quarter mile in 12.8 seconds/108mph keeping me pinned to the seat!!!), and he loved it when pictures literally fell off of the walls which developed new cracks in the sheet rock from the abuse. So, if you have the inclination, and want to listen at ear shattering levels, perhaps it would be worth trying. I'm happy with my near field listening at low levels; but I'm just an old guy......................

I've never had much luck with triode strapped pentodes such as 6BQ5 without feedback. The sound was a accentuated sharp/shouty midrange to my ears. I may have done something wrong being a rank amatuer, but I always had better luck using the 6BQ5 in pentode mode, with a dedicated screen supply or screen tap on the OPT, and some sort of feedback applied. Directly heated triodes without feedback do have a bit of accentuation in the midrange, but not with a sharpish bite that a strapped 6BQ5 has...in my experience. I'd venture to say good single-ended pentode mode 6BQ5 circuit with proper feedback applied, can sound closer to a DHT amplifier than a triode strapped 6BQ5 circuit. I dunno...there is this euphoria going with the sound of a directly heated triode such as a 2A3 or 45 that a indirectly heated 6BQ5 doesn't seem to quite do. To my ears. Never tried triode strapped 6V6. With published curves in triode mode, it may be worth a shot. Mike The 6BQ5 does not make a good triode imo as it is hard to get the distortion down to an acceptable level with currently available output transformer impedances. That may account for the shouty midrange that you describe. As a pentode, as you mentioned, it functions much better. SEPs, with some voltage feedback at the ouput stage only, can mimic the midrange and top end smoothness of a triode while preserving the bottom end of pentodes. The 6V6 as a triode isn't bad, but you would do better to go with a 6L6 or 6Y6. They will provide a little more power with reasonably low distortion if the operating parameters are calculated correctly. Also, much depends on the output transformers used. Perhaps I'm strange, but I generally like the Hammond offerings. For triode operation, the 16--SEA series does a great job. For those on a tight budget, the 125 SE series also does a good job (better with pentodes than triodes imo). Some folks like the Edcor transformers, but I've never heard them.

The extreme efficiency of the K-horns and La Scalas causes them to be very revealing of any kind of noise in the audio chain. The other guy's Mac 2105 and preamp may have the same, or possibly even a higher, noise figure as yours but it wasn't audible due to different tweeters or a less efficient speaker design. Is there any way he would bring his Mac and preamp to your house for a comparison with your equipment? I'd bet that you do not hear less hiss than with your own equipment, assuming that your Mac amp/preamp is operating within spec.

The ASR-433 is absolutely worth having restored! It's a terrific amp which should provide really enjoyable listening. Stromberg-Carlson was always known for turning out high quality products (their radios were wonderful). Glad to hear that you are getting one, especially if it is in good condition.

Yes, it is! Here's a brief explanation of the technology and how it evolved: http://www.tubesandmore.com/scripts/foxweb.dll/extpage@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?page=TECHSPEAKER01

If you try the repair shop verify that the person who checks it is familiar with vintage tube type electronics. A possibly better alternative is to find a local ham radio club which is sure to have some "old timers" (like me!!!) who are very familiar with tube electronics and their associated high voltages. Hams are generally more than willing to help out anyone who asks, and the collective knowledge in many clubs is quite formidable!

If you are not familiar with proper safety precautions for working with potentially lethal voltages, don't try it! Where are you located? Perhaps there's a knowledgeable forum member in the area who can check this for you.

A couple of places which have the 7189A: https://www.tubeworld.com/7189.htm http://www.tubedepot.com/pe-7189a.html http://www.tubemonger.com/NOS_NIB_Siemens_E84L_7320_prem_EL84_Munich_Prod_p/451.htm

This receiver runs the output tubes very hard (i.e. plate voltage actually exceeds the design maximum value by a few volts). I'd definitely stay with the 7189A. NOS tubes can be quite costly, so check the specs of the replacements currently being manufactured to be sure that the rated plate voltage is around 440-450, with a plate dissipation of 13 or more watts.

Don't feel that you must go with DHTs to get wonderful triode sound. Triode strapped pentodes can also do an amazing job. Check out the offerings from Decware before you make any definite decisions. http://www.decware.com/newsite/tubes.html

Which GE model do you have? I have a GE which is horrible when it comes to cleaning dishes which weren't pre-rinsed! The old builder's grade Maytag which I had before putting in the GE was amazing in comparison!!!

You can get the manual from Tubesound: http://tubesound.com/manuals/

It isn't just La Scalas which allow an incredibly satisfying low level listening experience, and biamping is not necessary either. For years I have advocated low level near-field listening as a wonderful way to become totally immersed in the music. It has the advantage of eliminating many, if not most, of the room response effects which can cause blurring of the sound and poor imaging; and, with careful speaker and listener placement, can allow a 180 degree soundstage of amazing depth. The ability to close one's eyes and actually be able to place vocalists and instruments in such a wide soundstage is simply wonderful! In addition, listening at low levels keeps the distortion of the speakers and amps (particularly SETs) driving them at very low levels as mentioned above. I use RF-15s and generally listen in the low to mid 60db range with peaks very rarely exceeding 70db. In spite of the small size and limited low frequency response of the speakers I still get very usable and subjectively strong bass output down to 40 Hz (which is low enough for me!). People experiencing this type of listening for the first time are usually amazed (even more so because I prefer to demonstrate this with only 1-2 watts/channel- tubes only, of course).

Sweep generators are used to align the IF stages of TVs and FM receivers, and often the crystal filters of vintage communications receivers. It "sweeps" the frequencies on either side of a set center frequency in a linear/constant amplitude manner. By observing the operation of the IF stage or filter on an oscilloscope, the desired bandwidth can be precisely adjusted. This is needed for proper rejection of signals from adjacent frequencies which would otherwise bleed into the frequency that you are listening to (or in the case of a TV, watching!).

Thanks Erik, but I did finally find the schematic for it (originally, I thought it was stashed with the schematic of the Laurel 300B). And Bruce, that filament voltage is terrific and should give you extremely long tube life! Well, back to the bench to repair my son-in-law's vintage Sony STR-AV1000 solid state (yuck!!!) receiver. I think he hasn't switched over to tubes just to torture me!!! Maynard

Pull the rectifier tube before doing this test to provide a greater safety margin. Doing so will result in a slightly higher reading of the filament voltage since the power xfmr won't be loaded down by the plate current/filament draw of the 2A3, and filament draw of the rectifier. Also, the voltage you measure will depend on the line voltage coming in, so it's worth measuring what's coming out of the wall socket too. For tubes like the 6SN7, you don't want the filament voltage under the worst possible circumstance (i.e. the highest power line voltage that you are likely to experience) to exceed 10% above the rated 6.3V. I'd also check the filament voltage of the rectifier which should be around 5V +/- 10%, and the 2A3 which should be 2.5V +/- 10%. If you find that everything is running too high and don't want to get into modifying the filament circuits, pick up a simple variac and dial down the line voltage a bit to create the needed operating conditions. (Also, when working on powered equipment, it's always a good idea to follow the "one hand in pocket" ritual. It prevents you from accidentally being grounded with one hand while you measure with the other- comes in handy if the measuring hand accidentally slips and touches something inappropriate!).

Thanks for the gracious offer Erik, but I'm not the guy with the Moondogs! It's Neo33 who is experiencing the technical difficulties. You and I are in agreement on all of this, and I am also waiting for Neo to post again with the results of his under-chassis examination of the wiring etc. Isn't this insanity fun??? Regards- Maynard

Have you ever checked the filament voltage with the 6SN7s installed? If it is running at more than 7V, tube life is likely to be considerably shortened.

7.8V no load in the filament circuit is reasonable. As Erik so importantly stressed, be sure that the high voltage electrolytics are discharged before you stick your hands in there (and of course the obvious- be sure the amp is unplugged)!!! Feel free to email me with any questions, or if you want any advice about how to easily and safely discharge them. With all respect for your EE degree, many of the EEs I've known and worked with "cut their teeth" on low voltage circuits and tend to have a bit too cavalier an attitude when working on HV stuff! Having on rare occasion gotten my fingers on the wrong side of a TV horizontal output tube plate circuit running at a few hundred volts, I can tell you that it isn't an experience that I'd recommend to anyone!

That's strange as the 6SN7 filaments should be wired in parallel, resulting in an identical reading at both sockets. I'll check my archives as I recall having a Moondog schematic and will email you shortly. Maynard

Erik's point about the orientation of the socket key is well taken (I should have had some coffee before posting!). I was referring to a top-side measurement with the key facing toward you. Measuring the two pins immediately to the left of the key when so oriented puts your meter across pins 7 and 8 of the 6SN7 and corresponds to the filament wiring in the tube. Equally well taken is the advice about not getting underneath the chassis unless the electrolytics are discharged; iirc, Ron Welborne did not show any kind of bleeder resistors across the electrolytics in his schematics (an absolute imperative in any high voltage circuit); and one certainly can't rely on the residual filament emission after power-off to properly discharge the caps. So, again, checking the filament supply status as I outlined previously is still quite safe and easy to do from the top of the amp chassis. The chances are you will not find much if any DC on the filament pins and the probable cause is a bad bridge rectifier. If the electrolytic after the bridge is very large (I have often used as much as 40k uf for such purposes) it's possible that the start-up surge current could take out one or more sections of the rectifier. It's highly unlikely that the filament winding of the power transformer has opened or that the electrolytic cap has shorted or developed so much leakage that the filament supply is basically being shorted to ground.

There is nothing wrong with the tubes. I tested all of them on the good Moondog and they all work fine. I wanted to know how would I go about troubleshooting the bad Moondog. What is the first thing I should be doing? The rectifier and the 2A3 tubes both lit up fine. Both 6SN7s do not light up at all. What make them not light up? It was working fine then it stop working. Adjusting the balancing pot can't possibly damage the circuitry of the 6SN7s. If you have a multimeter, there's a quick safe test you can try. Remove the rectifier tube so no B+ will be on any of the tubes. Then remove both 6SN7s. Power up the amp (the 2A3 will still light up which is of no concern for the short period needed for the test). Set the multimeter to a low DC range (or to autorange if available) and insert the probes into the first 2 pins to the left of the alignment key in the socket (the small notch between two of the pins). If you read approximately 6 volts (it doesn't matter if you read + or - when doing this), then you know that the filament supply is working. If there's either low, or no DC, switch to a low AC range and take a reading. If you get anything over a minimal amount of AC (or no AC either), then you have a problem in the filament supply and need the help of a technician to effect a repair.

An extremely cheap and effective alternative to "real" stands is to use cinder blocks. You can easily mount a wooden platform on the top of them, or just sit the speakers on top with a cloth underneath to prevent scratches. I've used them forever by covering them with color coordinated cloth to match couches, chairs, etc. If you are handy with a sewing machine you can make really decorative "socks" to put right over them. They don't resonate and don't move due to their weight. Might be worth a try.

I'm tending to agree with Russ. Given that it shuts down the same with the other generator, yours probably isn't the problem (it would be weird if both were way below 60 Hz). Why not grab some hearing protectors (get everyone out of the house!), connect the speakers at home, and see if it does the same thing. That will answer the question.