Hello, to what extent the rectification by diodes influences in the sound of an amplifier of tubes? Thanks, Martin:thmbsp:

Well I am no expert, but my Grommes amps have SS rectifiers. Having heard both tube and SS, I would say that the low impedance SS rectifiers really give it a kick. I definitely notice a difference in the bass slam and dynamics compared to a pair of Dynaco Mark III's I auditioned - which had a softer bass. Of course the Grommes amps are 100 watts and are stable to 1.4 ohms, while the Dynacos are 60 watts.

Well I am no expert, but my Grommes amps have SS rectifiers. Having heard both tube and SS, I would say that the low impedance SS rectifiers really give it a kick. I definitely notice a difference in the bass slam and dynamics compared to a pair of Dynaco Mark III's I auditioned - which had a softer bass. Of course the Grommes amps are 100 watts and are stable to 1.4 ohms, while the Dynacos are 60 watts.

Hey-Hey!!!,
Your experiments may not be the most thorough...:) The Mk.III has the typical wimpy Dynaco power supply, and its so-so output. It wouldn't suprise me at all that the Grommes was a higher quality amp, with better Iron and circuit design.

There are reasonable differences, and power suppliles can be made well with both. There is also the Hg-vapour types that behave like SS with regard to their impedance curves. There is also the divide in SS between PN junction and Schottky type. I have found that the Schottky delivers the vacuum-diode clarity I don't hear with PN junction types and their wacky turn ON/OFF characteristics...even those that do it softly in a few tens of nano seconds.

When building valve amps, I pick the Schottky for stuff like bias supplies. When the voltage rules out Schottky diodes( with PIV of 1k2V ), there are lots of vacuum diode options, along with the pretty Hg-vapour. If the amp is supposed to glow, a Thoriated filament WE diode can be designed around too. They're like 845 and 211 but w/o the control grid.
cheers,
Douglas

Pak,

You are right. The Grommes amps have massive transformers, and the Dynacos would run out of juice pretty fast - driving Maggies. It is an apples and oranges comparison. Here is a pic of the Grommes (the one in the pic is actually the identical Frazier F106C).

http://i17.tinypic.com/30nbzwh.jpg

Now you have me wondering if I have the PN junction or Schottky type.

Tube rectification is reported to sound good. I liked it in my ST-70. But diodes are not as wasteful as tubes; tubes drop (waste) a significant percentage of voltage.

Diodes can work well if you select soft recovery diodes (there are 600V rated soft recovery diodes). And for the little nasties left over you can add a reverse recovery spike filter on the input of the transformer.

As always, YMMV!

That Frazier looks identicle, down to the last detail to a pair of Grommes G-101a's that I was given. The guy said they worked when he disconnected them. Are they worth restoring? Simple circuit, so I can't imagine they would be difficult to fix up. I have read, but not confirmed that the irons are untralinnear? How do they sound compared to other tube amps?

Hey-Hey!!!,
That amp makes the Dynaco look primitive. Looks like a regulator for the g2, and I love those little sweeps. At only 17W each of plate dissipation, that's about equal to a pair of 6550's. The plate voltage rating is in the kV though, so it's taking advantage of those special finals...:)
cheers,
Douglas

Tube rectifier yields a mellow but sweet sounding, liked by many classical fans that demand the sweetness in the vocal and string reproduction.
SS rectifier yields a strong and positive sounding preferred by pop and big orchestra music fans.

Grommes must be very well built? Fired right up from a 30-yr sleep. And holly S&!? !!! She drove my a/d/s L-1290's with AUTHORITY. Pretty scarey voltges at ~850 V! This thing is a beast...

ebitda,

Those amps have power in spades. Good to hear that they are driving the A/D/S's with gusto. I like the way mine drive the MMG's - Total control, and deep tight bass (at least as deep as MMG's can get).

The G101a's are amazing for their going rate. You can find them for 200-350 dollars every now and then. The build quality is top notch - how many vintage tube amps are stable into 1.4 ohms?

Hey-Hey!!!,
That amp makes the Dynaco look primitive. Looks like a regulator for the g2, and I love those little sweeps. At only 17W each of plate dissipation, that's about equal to a pair of 6550's. The plate voltage rating is in the kV though, so it's taking advantage of those special finals...:)
cheers,
Douglas

Grommes made some great stuff that is under the vintage radar. The regulator is an OA2. I don't know much about the 6gt5 sweep tubes. Info on them is scarce. Mine did come with NOS Amperex's, but I have not been able to locate anything besides RCA for replacements.

A friend of mine has three of these... monster amps! Schematic is online at http://www.angelfire.com/vt/audio/

The Amperex ones may be RCA as well. 6GT5s have gotten pricey... as far as I can tell, the 6GT5 is equivalent to 6FW5 or 6GW6, both of which are dirt cheap octal tubes, the latter one with a plate cap. Another possibility is to add a 6 or 12V transformer in series with the heater winding and run 12GT5s or 17GT5s.