Glenn Studio Amplifiers

That's correct Ken.

Glad to hear that! Although Glenn send me 2 pairs of rectifiers, so far I have only used 1 pair and based on your feedback, they will stay until they stop working.

Thanks.

 

For sure, I was speaking very generally using my ears and gear.

But it is important to remember that whether B+ is actually "higher" depends on the amp one is using. And in order to know if B+ is actually higher, it is necessary to know which rectifier the designer built the amp around. For example, if the designer used a GZ34, with a published vdrop of 17 volts, then almost every other rectifier out there would result in a "lower" B+. On the other hand, if the designer used a 5R4GY, with a published vdrop of 67 volts, almost every other rectifier out there would result in a "higher" B+.

And thanks for sharing your experience with other SS rectifiers. HEXFRED rectifiers are supposed to be among the very best of the SS rectifiers, sounding more like tubes, but as I haven't heard any others, I really don't know how they compare. I can say that in my amp, the tonality of the HEXFRED is very similar to the Cossor 53KU, but with slightly better detail.

A bit more data... in my amp, with the Cossor, B+ is about 6 volts less than the designed value and with the HEXFRED, B+ is about 16 volts higher. For comparison purposes, it would be interesting to be able to hear a customized HEXFRED with a built in vdrop of about 16 volts.

 

Wouldn't we all like to know!

The usual reason suggested for the differences in tube rectifier is the differences in impedance of the said rectifier which leads to differing voltage drops an consequently different plate voltage B+. The rectifier with lower voltage drop would have a lower PS output impedance and also the higher plate voltage would shift the amp towards a higher conducting operating point, both supposedly positively changes.
So, like @gibosi suggested if an amp was designed with gz32 in mind (like mine), then on using GZ34 would provide higher plate voltage and the sound would supposedly be faster and clearer and on using a rectifier with higher voltage drop like 5R4, the sound would slower and softer.

Unfortunately, that just hasn't been my experience. The directly heated 5U4/5R4/U52 sounded faster and clearer to me than the GZ32 or GZ34 even though the plate voltage was lower with them.
TBH, I myself believed that the lower impedance rectifiers would sound better for the reasons given above which is why I designed around a GZ32(cheaper than Gz34) and I had to overcome my own expectation bias before I concluded that for some reason the higher impedance directly heated rectifiers just sounded better.

The only thing that I could think for the higher impedance rectifiers was that may have slightly lower ripple than the low impedance ones ripple was hardly a concern in the design because of the big-ass choke and the contribution of slightly higher resistance towards lowering ripple would be minimal at best when compared to the rest of filtering.

@gibosi : Cossor 53KU is a nice rectifier - big powerful sound with great dynamics and resolution. It still has that IDH signature though,bit of bass bloom and not as clear as DH rectifiers. Infact, the SS rectifiers I have tried do not usually have that bass bloom but they are not as engaging as the 53KU either. I haven't tried the HEXFREDs though.

 

Tried a solid state rectifier today. Was earlier using a U52.

Not bad at all.
+ very airy, solid bass, a bit clearer, super cheap
- Flatter, grainy, headstage

 

I suggest we consider a similar question because the answer is likely the same:

Does anyone know the reason why double triodes from different manufacturers sound different?

After all, a rectifier is essentially a double triode without grids. I am quite sure you could hook up any double triode as a rectifier, leaving the grids disconnected, and it would rectify current, although probably not very well. Personally, I have always thought it very interesting that the Western Electric 421A double triode and the Western Electric 422A rectifier appear to be using the same plates and look almost identical. Perhaps the WE422A is simply a modified WE421A?

While I can't say precisly why double triodes sound different, I assume it is related to construction differences inside the tube. And further, I have noticed rectifiers and double triodes from the same manufacturer seem to have similar sonic signatures. The sound signature of RCA rectifiers reminds me of RCA double triodes. The sound signature of GEC rectifiers reminds me of GEC double triodes. And so on...

 

Power to the People

The last few posts have included terms that I'd not heard of until a few years ago. I thought some others reading this might be in a similar position so I've put together a few notes about amplifier power supplies. Hopefully they're of interest.

Background

The electrical signal that carries sound is AC. A pure DC signal will result in no sound at all from your headphones/speakers

Voltage Amplifier Tube
Two things are fed into a voltage amplifier tube: Direct current (no sound at all) and AC from your DAC/Pre (the signal that carries the music).
One thing comes out the other side of this tube: A stronger version of the AC signal that came from your DAC/Pre
Three parts (two in / one out) = triode
Sometimes there are two triodes in a single tube, in which case it's called a double triode.

What is a B+ Supply and What Does It Look Like?

The flat DC signal that enters the triode is called the "B+" voltage. "B" stands for "battery", as batteries historically provided this DC. If the DC that comes into the triode isn't pure (ie. it wobbles a bit) this will come out of the other side of the triode along with the music, resulting in an audible hum. Unless you're a masochist, you don't want this.

An ideal B+ power supply will provide a DC signal to the triode that is perectly flat with no wobbles at all. These wobbles are called "ripple".

The Anatomy of a B+ Power Supply

1. Mains Transformer
The electrical power coming out of your wall socket enters a transformer that splits it into parts for different purposes. One or more of these parts is dedicated to providing the power needed for the B+ (remember, perfectly flat direct current).

2. Rectifier
The power that comes from your wall and then leaves the transformer is AC. This needs to be changed into direct current. The component that achieves this is called a "rectifier" (etymology - it puts it right, fixes it up) and usually consists of a diode. A diode has two parts (as opposed to a triode) and can be either SS or a tube.

3. Filter
Once the DC leaves the rectifier it's full of wobbly bits (ripple) that sound nasty. The filter stage of the power supply gets rid of this ripple. Often this is achieved through the use of capacitors and either resistors or chokes. Ideally you'd have direct current leaving the other side that's totally devoid of ripple. Perfect for feeding the hungry triode that's amplifying your sound signal.


Note 1: There are other parts sometimes, such as a "regulator"
Note 2: I'm not qualified to do much more than read about electronics

 

B+ Power Supply in a Glenn OTL

1. Mains Transformer
All transformers emit a magnetic field. These can be quite annoying as they can interfere with the DC and add more wobbly bits to it (hum). Glenn currently uses Lundahl transformers that have only a very small magnetic field and this field is further shielded by a metal housing. The result? Minimal impact on the B+ resulting in no audible hum.

2. Rectifier
To my knowledge Glenn has used 5 volt tube rectifiers (eg 5U4G), TV damper diodes (a type of tube eg PY500A) or solid state (HEXFRED diode) rectifiers. These each have their own attributes.

There are lots of 5v rectifiers that can be substituted for each other. This type of rectifier is good if you want to roll tubes. One possible disadvantage is that you need to be careful of the current coming out. It can potentially limit the number/types of tubes you can use in the other positions. Check with Glenn if you're not sure that your rectifier is powerful enough.

The PY500A that Glenn uses has very few tube rolling options. It's more efficient than the 5 volt types, dropping very little voltage as the power passes through it. Another advantage is that it can provide much more power to the other tubes.

The third type of rectifier than Glenn uses is the HEXFRED diode (or, rather, a combination of them), which have a reputation for being one of the best solid state options. There are no tube rolling opportunities here, but they are the most efficient of the three types and provide negligible voltage drop. Some prefer the sound of SS rectifiers while others prefer tube.

3. Filter
The filter Glenn uses in his OTL to eliminate ripple usually consists of three capacitors and two chokes. They are positioned in this order (electrically): C - L - C - L - C (where C = Capacitor and L = Choke). Chokes are more expensive than resistors but are generally considered to be superior.

Please correct me if I'm wrong in any of this @2359Glenn

 

Glenn is a match maker. Soon he'll be bringing together these two star-crossed lovers.

 

Your amp will have built in HEXFRED diodes 4 of them in a full wave bridge.
No tube rectifier or socket.

 

What is the configuration of the HEXFRED rectifiers you build that fit into a 5-volt octal socket? I would assume that they are comprised of a single HEXFRED diode? And not a full-wave bridge with four of them?

 

The 5 volt tube rectifiers Glenn uses in the OTL are dual diodes and, I assume, are used together to form a centre tapped full wave rectifier. I'm guessing, then, that Glenn would use 2 x HEXFREDs to make this SS rectifier function in the same way.

A single HEXFRED diode would only result in half wave rectification. I don't think Glenn would use four HEXFREDS either to form a full wave bridge. From what I've read in the last few hours, either of these two alternatives in an amp designed for centre tapped full wave rectification would mess up the B+ circuit entirely.

A few hours reading. That makes me an expert, doesn't it? Note the use of the verbs "guess", "assume" and "think" in the foregoing crap.

 

Gibosi

You have 2 diodes in your HEXFRED adapter. Your amp has a center taped transformer 560 volt center tapped.
Output or rectifier to filter will be 280 volt pulsating DC.

 

Glenn sent me a teasing image of my amp layout five minutes ago. Thought I'd share it with you:



My face hurts from smiling.

There is joy in researching, planning and saving. I'm at the excited anticipation stage now. All these steps should pale into insignificance compared to the experience of listening to music through this.

Thanks @2359Glenn ! You've made my day.

 

• Monster Clarity Cap TC-2 instead of electrolytics

 

Anybody with Glenn OTLs and EC Super7 ever compare both of them?

 

Nathan: What do you think you'll do with the pre-amp outputs?
Glenn: I was going to take them straight off the C3g/6SN7 plates, but might add a cathode follower. Will see if I can squeeze in another socket.

@2359Glenn I think I'll take to calling you "Dr Who". Somehow your amps must be bigger on the inside than on the outside. Thank you, my friend.

 

I ordered my amp in March 2015. The nineteen month wait has allowed me to save up my pennies.

Cheap | Quality | Fast : You can only expect two out of three. Glenn has a demanding full time job, so we need to be patient. As far as I'm aware, he built a total of four amps in 2015 and, so far, has completed three amps in 2016. When will number four roll off the assembly line @2359Glenn ?

Are you still looking at getting a new amp from Glenn @JoelT ?

 

Tubes of the same type but of different manufacture may sound different for several reasons, a few of which are:

1) The inter-electrode capacitance may be slightly different, which causes different RC constants. The Miller Effect, which multiples the actual capacitance by the tube's gain, can alter these constants.

2) The cathode coating is slightly different (varying amounts of barium, strontium and calcium) resulting in slightly different behavior that is close enough to function as a tube of a particular type but not so close that the small difference isn't audible.

3) Differences in ions. Many of the tube materials (metals and the mica) absorb or adsorb gasses and contaminants which then migrate out when the tube is used. These can attach themselves to the grid causing grid current flow.

4) Different mounting techniques for the internals make the tube more or less microphonic.

5) Differences in the alumina insulation on the heater (thicker, thinner, fractures, etc.) may cause more or less heater-to-cathode leakage.

6) Different grid pitch and materials can slightly alter the mu and Gm.

7) The more someone pays for a tube the better it sounds.​

Even tubes of the same manufacturer may sound different batch to batch, and the quality control considerably varied.

Yes, take a signal tube and strap the grid to the cathode and you've made a rectifier.

Rectifier's don't have a sound, per se. What they do have is varying voltage drop and varying current carrying ability, and some are more or less tolerant of overload conditions. So when a rectifier with a greater/lesser voltage drop is substituted for another the B+ may change which may alters the position of a signal tube on its load line making it more or less linear for the given B+ and current load. Same thing for over-current situations. All of this can show up as sound. Guitar amplifiers, in fact, often sound best when overloaded as the drop in B+ (aka sag) improves the distortion. This is why some players crank the amplifier to maximize the load and thus the voltage sag and ensuing distortion.

 

So given how long it generally takes to get a Glenn amp, it's a near miracle I now suddenly find myself in possession of two. I have a GOTL (non-Lundahl), and a GEL3N. Both are incredible values imho. Thanks to Nate for starting this thread and introducing me to this!

 

Lucky bastard!