help please
Hi there folks,
Not being an expert on tubes, but being the proud owner of a pair of late 50's Quad 2 monoblocks, I have a question about the rectifiers.
I think the original GZ32's have been replaced (before my time) by GZ34's, as they don't have the traditional coke-bottle shape, but I can't tell for sure because there are no obvious markings anymore.
Also, I can tell from looking at them that the rectifiers are different - I guess they are either different manufacturers or age or internal construct (e.g. getter types), or all of the above.
So, is it necessary or preferable to install a pair of the same manufacturer / internal construct, or doesn't it really matter because a rectifier is a rectifier so long as it works?
Many thanks for any advice
J
Hi there folks,
Not being an expert on tubes, but being the proud owner of a pair of late 50's Quad 2 monoblocks, I have a question about the rectifiers.
I think the original GZ32's have been replaced (before my time) by GZ34's, as they don't have the traditional coke-bottle shape, but I can't tell for sure because there are no obvious markings anymore.
Also, I can tell from looking at them that the rectifiers are different - I guess they are either different manufacturers or age or internal construct (e.g. getter types), or all of the above.
So, is it necessary or preferable to install a pair of the same manufacturer / internal construct, or doesn't it really matter because a rectifier is a rectifier so long as it works?
Many thanks for any advice
J
Such innocence! This is a debating point on this forum.
My view is that the main issue with rectifiers is lifetime/reliability. If it changes the sound then there is something wrong with the rectifier or the amplifier design. Others will disagree.
As you have a 1950's British classic amplifier, you might wish for aesthetic and historical reasons to use a 1950's British classic brand of rectifier - but take a deep breath before looking at prices, and beware of fakes.
Hey there,
apart from all the metaphysical 'I can hear the grass growing' stuff, it might really matter, as different rectifier tubes will surely have a different forward voltage drop under load conditions - causing the B+ to sag differently in both amps in signal peaks.
Would be unusual if this would be inaudible...
Greetings,
Andreas
Maybe its just me, but NONE of the HiFi amps I have designed have needed or wanted any feedback. Pete's red board uses Schade feedback to lower the output impedance of the pentode output tubes. That type of feedback in that application proves useful. Some guitar amps use feedback to control the tone.
I tried it in my SSE and have now removed the CFB switch and permanently wired it for triode.
IDK if it's speaker dependent, but CFB sounds much worse with my single drivers in either UL or triode mode.
I still have the switch in mine, and it does get used when I need to squeeze 14 watts of Pink Floyd through my 15 inch Silver Iris. I normally use the SSE in a small room with 88db Yamaha studio monitors. KT88's in triode sound the best and go loud enough for any music. The SSE in UL with CFB through the 15 inch OB's can make bass heavy enough to be heard inside the house across the street. I now use a 125 WPC version of Pete's red board to really annoy the neighbors. It can slap the 15 inchers around without feedback.
For a new build, forget about the overpriced GZ34/5AR4. Try two 6DE4 (or any of the high current TV damper diodes) in a full wave center tap circuit, or 4 of these in a bridge. Suggest a separate filament winding (or transformer) for the full wave CT since the cathode is at HT. If you do a full wave bridge, three filament transformers should be used since two tubes have AC applied to the cathodes. The damper diodes draw approximately 1 to 2 amps apiece, but filament transformers with 2500 volt insulation should not be "bank busters". Old TV power transformers (like the ones from old RCA CTC series TV's with the two 5U4 rectifiers in parallel) make good power transformers for medium power audio gear...and they have multiple filament windings.
Why deal with the fuss of a 4 vacuum diode bridge, when a hybrid bridge made from a pair of dampers and a pair of 1200 PIV Schottky diodes is: "noise free", avoids the doubled forward drop, and doesn't have filament supply issues?
For high current B+ supplies, the 6CJ3 is (IMO) the vacuum damper of choice. A 6CJ3 in 1/2 wave rectifier service is good for 350 mA. of DC. At least twice that much is available from a hybrid bridge setup.
For high current B+ supplies, the 6CJ3 is (IMO) the vacuum damper of choice. A 6CJ3 in 1/2 wave rectifier service is good for 350 mA. of DC. At least twice that much is available from a hybrid bridge setup.
Most TV damper diodes can be operated from the same heater supply as the rest of the amp if this is needed. They have high H/K breakdown ratings and this is how they were used in the TV set they were designed for.
The damper diode rectifies the excess energy in the flyback transformer and stacks (bootstraps) the recovered DC voltage on top of the B+ voltage to create the "Boosted B+" or "Boost" voltage supply in a TV set. The cathode operates at the Boost voltage. In a large color TV the B+ was about 375 to 400 volts and the filtered low current Boost voltage was 600+ volts for the CRT screen grids. The damper tube also supplies the AVERAGE current of the horizontal (line) output stage which is 200 to 300 mA.
In a 6.3 volt heater string TV the heater circuit was typically grounded. This is good practice just in case a damper tube H/K short occurs. Series string TV's ran the heaters directly from line voltage.
I have used damper tubes in sweep tube guitar amps. I ran the tubes from a common 6.3 volt transformer with one side grounded. B+ came from a 480 volt industrial control transformer. I built those amps about 15 years ago and I believe them to be still running, but I haven't seen them in several years.
Actually most TV damper diodes have a rather low max. H to K maximum voltage rating in one way (heater positive referenced to the cathode) in the order of only +100 to +300V (peak). A separate heater winding is allways recommended with cathode connected to heater at one side. It must also be remembered that TV damper diodes were not made (nor recommended) for mains supply frequency (50/60 Hz) rectification and worked at TV horizontal (line) scanning frequency with very short duration pulses. (max. ratings given by RCA are for 10 microseconds pulses). For operation at 50/60 Hz some derating will be needed (especially with higher value filter caps) but such datas were never published because the tube was not initially intended for that purpose. TV damper diodes are very rugged and reliable if not pushed too hard, just keep in mind some limitations and don't rely too strongly on the published maximum ratings which are for completely different operating conditions.
And by the way, if safety is your concern, there are many single ended (without top caps) damper diodes available in novar or duodecar (compactron) basings. (6CL3, 6CK3, 6DW4, 6CE3, etc...) and they are dirt cheap too. (A good reason to use them)
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Eli...you may remember from the ARRL handbook and other ham radio magazines (from 1963 or so) that some of the 6146-based home brew transmitter schematics specified a 800 v transformer and a bridge rectifier using a 5U4 and two 6DE4 tubes. Old color TV power transformers worked fine for this. It may have been precaution, but I always used separate filament transformers for the damper diode tubes and tied the cathode to heater nonetheless...if the 6DE4 had a H-K short, didn't make any difference.
I will have to try the Schottky diodes...have any good numbers that work at 2 kV PIV or so? I understand these rectify better than the 1N4007's in series...
I will have to try the Schottky diodes...have any good numbers that work at 2 kV PIV or so? I understand these rectify better than the 1N4007's in series...
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