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EL84 Amp - Baby Huey
EL84 Amp - Baby Huey
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Old 14th March 2008, 04:47 AM   #391
chrish is offline chrish  Australia
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Thanks Ian,

My problem is that I would like to use the 5 volt winding to run the filaments of a valve rectifier, so I am looking for an alternate power source for the CCS. Looking at the schematics again I see that I have made a small mistake, the power supply is -14 volts, as you mentioned. I have a 7915 regulator also (-15volts). You mentioned last November to one builder that wanted to build valve rectification to use the 50 volt tap to supply the CCS since the 5 volt tap was being used to run the rectifier filament, hence my initial interest in this approach.

My limited electronic knowledge leads me to think that if I am running a valve rectifier, the B+ will be riding on the filament voltage. Is this correct? If so, I am assuming that running the CCS supply off this 5 volt filament tap is not going to work.

I have the parts in the parts box, the little transformer is only 40mm * 35mm * 35mm and I have plenty of room in my chassis to go with a simple regulated -15volt supply.

As I stated, my experience is limited, so not sure if I am pointing in the right direction

BTW, when you mentioned in a previous post the stuff you were doing at work, combined with you living in Adelaide, made me think DSTO. I did some work with them in a previous life flying some of their projects in HS748s.

Cheers,

Chris
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Old 15th March 2008, 02:22 AM   #392
kd0bdk is offline kd0bdk  United States
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Default tube and circuit selection

regarding tube selection, the 6sn7 type tubes are very high quality, but for more gain, try the 6sl7 type of dual triode. for a novel approach, check out the 6bm8. ihave seen concern about power 'pentodes" (6k6) versus power "tetrodes". power pentodes have a larger plate and 3 physical grids, and the grids are alligned so they are in a straight line so that they shield one another...beam pentodes are sometimes mistaken for tetrodes because they have only 2 physical grids, but use beam forming plates to serve as a virtual suppressor grid, and so may be considered as a pentode class tube in most respects
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Old 16th March 2008, 06:14 AM   #393
kd0bdk is offline kd0bdk  United States
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regarding rectifiers; ive run across more than one 6bq5/el84 pp amp using a 6ca4 tube as arect...the isolated cathode and 6.3 volt/1amp fil of the 6ca4/ez81 rectifier make it a handy match, andby using a pair of 6ca4's with series fil's andplates in paralel can give considerable flexibility...put p1/v1 to p1/v2, p2v1 to p2/v2 , k/v1 to k/v2
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Old 16th March 2008, 07:11 AM   #394
chrish is offline chrish  Australia
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Thanks for the interesting suggestions re the 6CA4s. I will admit that my interest in using a valve rectifier is one based largely on aesthetic rather than technical reasons. I have a couple of Soviet 5U4Gs and would like to use one for this project. I will, however, keep your suggestion in mind for future projects.

Cheers,

Chris
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Old 16th March 2008, 07:40 AM   #395
kd0bdk is offline kd0bdk  United States
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Default post377

regarding the dual-sheet-beam pentode-it dores still require a ballanced dual signal to function properly...i suppose that you might bias both grids at some point of about 2 to 4 volts, then apply signal only to one grid, but you could basically see the same thing with a long tailed pair...2 identical triodes, for example, sharing an unbypassed cathode resistor, both grids biased at the same voltage, a 1meg resistor between grids, a "large" cap from one grid to ground, the other grid receives the input signal. an appropriate matching plate resistor as plate load and then cap coupling to each grid of the next stage...i have seen this circuit used in the output stage having 6k6's, gibson used it with 6v6's, and i have seen it usud with 6L6gc's...remember, tho...the ONLY way you can use this arrangement is to bias the long-tailed-pair as class a!!!


you can also use an active splitter (class a) by using 2 triodes as a ballanced driver for a pp output by using appropriate plate load resistors and coupling the plates to the grids of a pp output stage...one triode gets a signal applied to the grid, the other uses a 50/50 between the output tube grids for its grid signal...the voltage divider provides considerable feedback to the second triode, as well as a near perfectly inverted signal which is very forgiving to any slight mismatch of parts...if you don't mind a bit more necessary drive, you can add a shared, un-bypassed cathode resistor to the phase inverter triodes...
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Old 16th March 2008, 08:14 AM   #396
kd0bdk is offline kd0bdk  United States
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Default post389

a 7812 or 7912 would give 12 volts...you could use diodes to drop the excess voltage...some drop .6volts, some as much as 1 volt... do NOT use zeners...they will catch fire unles used only as a voltage ref for an amplified (regulator) circuit. i need the tube types to calc. the current, but a bias winding generally puts out only an extremely small current...fils are usually the heaviest current draw...
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Old 19th March 2008, 08:37 PM   #397
boywonder is offline boywonder  United States
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I have about a dozen medical power entry modules (Schurter) that have the IEC power entry module combined with a power switch, fuse, and a medical RFI filter. Will this medical RFI filter on the AC input help or degrade the design? Should I just stick to a separate switch, cord entry module and fuse?

These medical power entry modules are tempting because I already have them and they are collecting dust....I can post a pic of the filter and the RFI specs when I get home, if required.

I bought a pair of 8H 100 ma chokes for the dual mono power supplies; however, now that I am hip-deep in Morgan Jones' book, he suggests sizing the current capacity of the PS choke for the post rectifier AC current as well as the DC current. Using this calc, it would appear that I need a roughly 150 ma rated choke for each supply....Is a 100 ma rated choke a problem here?

Finally, if I do xfrmr-rectifier-2mf-8H-220mf CLC, do I still need the 220K/2W resistor across the 220mf as shown on the schematic?
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Old 19th March 2008, 10:26 PM   #398
gingertube is offline gingertube  Australia
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boywonder,
The IEC Power Entry Module with the RFI Filter will be ideal. I use these myself.

The latest "Baby Huey" monoblocks I finished last weekend use the Hammond 8H 100mA chokes. I'm still doing final tweaks on these monoblocks but the chokes appear to be adequate although 150mA rated chokes would be better.

The 220K/2W "bleed" resistor across the final 220uF capacitor is always a good idea. It makes sure that the capacitors are fully discharged when the amps are turned off so that (as long as you wait 5 minutes) you don't get nasty surprises when you decide to make a mod or some more measurements.

Cheers,
Ian
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Old 20th March 2008, 12:37 AM   #399
boywonder is offline boywonder  United States
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Thanks Ian! Apparently, I wouldn't know a bleed resistor if one was staring me in the face.....makes perfect sense now...
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Old 20th March 2008, 04:18 AM   #400
dhsettim is offline dhsettim  New Zealand
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Default Baby Huey variations

Hi Ian,
I wondered, as a Baby Huey variation, that if a high current input/driver tube was used in the so-called E-linear configuration--ie connected to the UL OPT taps--could the Baby Huey cross coupled feedback thingy mechanism still be used? There will be two local feedback loops at work I guess, but I don't think that should be a problem.
As an extension of that "vapourware" (as AW calls it) what about using a pentode driver in E-linear with the screen (low current) connected to the output tube anode as per the BH? That at least would keep the screen voltage below the anode voltage. Then ya could even have two lots of BH feedback to play with.
Whatcha reckon 'cause I have no idea whether they would work.
best wishes
tim
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