Glenn Studio Amplifiers

Glenn has started making a new amp based around the EL3N pentode. It is switchable between triode or pentode mode, which has the effect of changing the output power. He describes it as sounding like a 2A3.





Rectifier - AZ4
Driver - EL3N
Output - EL3N
Power Triode - 1.5 watts at 32 ohms
Power Pentode - 3.5 watts at 32 ohms
Has Triode - Pentode switch on back
TRS and 4 pin XLR jacks for output
All Lundahl transformers
115 or 230 volt
Introductory price $1500.00 + Shipping

Apparently the EL3N tube is plentiful and cheap ($25 each) if you know where to look.

Personally, I think he's mad selling the amp this cheaply as the Lundahl output transformers and the Lundahl power transformer would have cost him about $1K. Great deal IMO and perfect for planars that the OTL can't drive. I'd buy it if I wasn't so heavily invested in an OTL.

Glenn says that it sounds almost as good as the $4k 300B amp that he builds, just with less power.

I don't think I'll get the chance to hear one, but I'd still be very interested to read impressions. I believe that he has a unit built and ready to ship.

 

Tempting.

 

Yeah, he built this for himself. But I guess he already has a V2.0 planned with a driver tube that has more rolling opportunities. The appeal of this amp is the fact there are no crazy tube rolling options. That way you spend more time enjoying, and less time scouring the internet for more tube to hoard, and drive more prices up...

 

@ButtUglyJeff

I think he is planning on keeping the same driver, just changing the rectifier to allow rolling there. This version uses a European side pin rectifier (in keeping with the EL3N) whereas subsequent units will have the usual 5 volt candidates. More rolling for those who are that way inclined.

Personally, I suspect that as the rectifier is there just to convert AC to DC and is then filtered to buggery, rolling will have little effect within a particular family. Different types though will result in various voltage drops and sags, affecting the B+ and therefore operating point somewhat.

I'd rather spend money on music than on tubes. Each to their own I guess. One of the beauties of buying a custom made amp is that you have choices.

 

Agreed. No Christmas Tree amps for me...

 

I am not an electrical engineer, so this is an intuitive understanding. I would absolutely welcome a better explanation.

Yes, in my experience, changing the effective B+ often changes the sound. Generally, higher B+ sounds faster and clearer, while a lower B+ sounds slower and softer. However, even if two vacuum tube rectifiers of the same type but from different manufacturers have the exact same voltage drop (as actually measured in the amp), they can and typically do sound different. After all, it is well documented that there is a tremendous difference in the sound of 5U4G type rectifiers, for example. And this has been my experience with other types, as well.

So sound differences due to vacuum tube rectifier rolling are not only due to vdrop and sag. There is something else at work here as well. (And this is where I put my lack of technical knowledge on display. lol) Vacuum tube rectifiers are not purely resistive devices. They also have a non-resistive reactance, a "frequency response", if you will. And it is my understanding that this frequency response modulates or "rides" on top of the rectified DC current. And this "modulated" B+ can and does change the tonality of the system.

But of course, if one is happy with the way the amp sounds with the stock rectifier, then by all means, save your money for music.

 

You would have to look at the B+ voltage with a scope and compare the two rectifiers to see what is really going on.
Even if you measured the voltage and it is the same it could be changing when the current changes under load.
Even two tubes of the same make really are not the same they were made by hand and there are little differences
in spacing in the tube.

 

My ears are not good enough to be able to differentiate between two tubes of the same type, made by the same company, at about the same time, with the same construction, and I think that is a good thing. I appreciate having spares and I am pleased that they all sound the same to me.

But I do have a 1944 RCA 5U4G and a 1949 RCA 5U4G, with significant construction differences, and they definitely sound different. And in total, I have rolled about 25 different rectifiers through my Glenn OTL, and again, they all sound different.

It is very clear to me that voltage drop alone does not adequately explain these sonic differences, but at this time, the definitive explanation is something I can only guess at.

 

How do you rate the HEXFRED diodes to rectifier tubes? I know the B+ voltage is higher with them.

 

I like the HEXFRED very much. Perhaps due to the B+ being 16 volts higher than your design value, the presentation comes across as very fast with excellent transient response. But that said, no one rectifier is the best with every driver/output tube combination...

And I wonder if a SS rectifier has a sonic signature? Unfortunately, I do not have any other SS rectifiers so I cannot test this. But I tend to think that with the HEXFRED installed, I may well be hearing the true sound of the driver/output tubes, alone, albeit at a rather high B+.

So I have begun to use the HEXFRED as a reference tool. Considering it as neutral, comparing it to various tube rectifiers gives me a pretty good idea of each tube rectifier's sonic signature. And the HEXFRED also helps me to predict which tube rectifiers might be a good fit for different combinations of driver/output tubes.

For example, with the HEXFRED, if the mid-range of a certain driver/output combination is somewhat subdued perhaps a rectifier that is a bit more forward, like a Holland-made rectifier, might be a good fit. Or if the highs seem to lacking in air, perhaps a rectifier with more air, like one of the GEC rectifiers, would be a good fit. And so on...

So I would encourage everyone who is interesting in rolling rectifiers to get a HEXFRED. I think it not only sounds great, it is also very helpful to me in understanding what I am hearing when trying out new rectifiers.

 

I have one mercury-vapor rectifier, an AX50 (that requires an adapter to drop 5 volts down to 4). The couple times I used it, it sounded pretty good. However, as it tends to arc unless preheated, it stays on the shelf. I have an idea about putting a few parts together to make a little preheater, but haven't gotten around to it yet. But now I am thinking maybe I should get to it sooner rather than later...

 

I have been rolling a few rectifiers in my OTL amp for last few months and would agree that the rectifiers do make a significant difference( atleast in a simplistic single ended amp like mine). On the other hand, some of my findings differ from the above posts.
I didn't find higher B+ to necessarily sound faster or clearer and vice versa . The patterns I did note were :

• Different brands of rectifiers of the same type do sound different and sometimes noticeably so.
• Usually the physically larger sounded more dynamic and layered than the smaller counterparts. For ex. 5U4G/5R4GY was usually better than GZ32/5V4G and 5u4G was better than smaller 5U4GB.
• The biggest difference though for me was how the directly and indirectly heated sounded in general. The DH ones were usually clearer and had tighter, better defined bass. The IDH ones sounded a bit loose and slightly veiled esp. in bass.

The SS rectifiers certainly have a sound and I usually find them a bit grainy and flat in terms of microdynamics and soundstage and ya, different SS rectifiers do sound different so I wouldn't automatically assume them to be neutral.

 

It would be interesting to find out the reason for these differences. Does anyone know? Do any measurements of the output after filtration correlate with the perceived differences, or don't we know what to measure yet?

Curious, not sceptical.

 

I haven't rolled rectifiers at all on my OTL as I thought any change in sound would be insignificant compared to rolling output tubes?

 

Are you happy with the sound of your amp? Is there some flaw that you want to fix? If so, in which direction do you want to tilt the sound? What tube/s will provide this sonic tweaking? These are the questions that you should be asking before starting on tube rolling, whether it be the rectifier, gain stage, driver, output etc.

Before I buy any audio equipment I read as much as I can about it, ask questions and, if possible, spend some time listening to it. The purchase of tubes should be approached in the same way. The danger in "tube-curiosity" is that it can be a big drain on limited funds that are better spent elsewhere. I've learned this the hard way.

When I choose tubes for my Glenn OTL in the coming months it will be with a purpose. What output impedance do I want? How will changing from C3g to 6SN7 affect gain? Which 6BL7 will give me the timbre I'm looking for?

The dedicated tube roller is a different beast all together. Perhaps for many of this breed music comes secondary to the sound of tubes. While this no longer appeals to me, the experience I've gained has been useful. I know what tubes I like and why (within a limited number of families). A tube roller that is able to discern the differences in sound and communicate these well has much to teach us. They can help us choose tubes that make our music sound more like we want without wasting time or money.

This post has become longer than I intended, sounds preachy and doesn't really answer the question. Sorry, Arnold. I just got carried away as it's something I feel strongly about. Just don't roll tubes for the sake of change.

 

Generally, the power and driver tubes have a more noticeable impact on the sound. This may depend on the amp, but I'd say generally that this is the case.

I was discussing rectifier tubes/SS components on Discord this week with some people, and I definitely hear differences myself. I use Telefunken rectifiers in my Zana Deux OTL as I found they sound the cleanest, whereas the Philips rectifiers I have sound warmer and a bit congested.

I've also tried Brimar tube rectifiers in the past and enjoyed their sound... It really depends on the amplifier and other tubes being used. I would agree with @MoatsArt in that it a personal philosophy should be employed. Sticking with stock rectifier tubes is also just fine, especially if you enjoy the sound of the amp. In the past, I started rolling tubes on my Woo gear, and found myself constantly seeking different combos, but never getting the clarity I wanted.

It seems odd that SS components wouldn't offer the best sound, especially for doing a simple task like rectification, but I think I'd take the tube option myself. Maybe it's the DC voltage level, maybe it's something to do with ripple, something is being influenced in a way that can be audible, depending on the amp design.

 

Nate

Yes, you didn't answer my question as it seems you were answering your own doubts. You will notice that I said I haven't rolled any drivers nor rectifiers because I do not roll tubes for the sake of rolling. Don't believe everything you read in the internet.

 

Exactly my thoughts but this talk about rectifiers in the previous post made me ask if I am missing something as I do not want to change my drivers and rectifiers if there will be no significant changes in sound.

 

I believe your amp came with 42EC4/PY500 rectifiers. Other Glenn owners whose amps use these rectifiers indicate that they hear no differences in sound from one brand to another. So yes, I think you are correct that any change in sound would be insignificant.

On the other hand, those of us whose amps use 5-volt rectifiers do hear significant changes.