Glenn Studio Amplifiers

This is my 300B amp from Glenn

 

@MoatsArt
Is your amp being built already? Do you know the status?

 

Glenn mentioned that he thinks he will be able to build mine sometime in (northern hemisphere) Spring. I believe that he has some more pressing things going on in his life at the moment, so probably best not to pressure him.

 

Right. Mine might be built in Summer then...

 

Have recently been running 6BL7 as output tubes. Adapters allowing either 2 or 3 6BL7 per 6AS7 socket are available on eBay.

Shown here, four early 1950's Sylvania 6BL7GT, a 12 volt FDD20 driver and a Cossor 53KU rectifier. Sounds terrific!

 

Hi @gibosi

Thanks for that! I'm curious about the effect of different tubes in the OTL. Have a few questions:

1. What other gear are you using in your chain?
2. Can you please list two or three common power tubes you have used in this setup (eg, Mullard 6080, RCA 6AS7G, TS 5998)
3. Please describe the specific sound produced while using these tubes (to give us a frame of reference)
4. Please describe the specific sound produced while using your 2/channel Sylvania 6BL7GT "flat plates"

This will make tube choice easier for those of us who don't roll. We need your experience!

Thanks

Nathan

 

Again, I am a tube roller/collector. I would not call myself an audiophile. Further, I do not have the temperment or the discipline to devote the necessary time and energy to discern and describe the "specific sound" of one tube and how it compares to the "specific sound" of another. Further, in my experience, how a tube "sounds" is very dependent on the other tubes and elements in one's system...

While I understand that there are those who do not want to roll, in my opinion, rolling is the only reliable way to determine what works and what doesn't work "in your system." A colleague very aptly compares tubes to ice cream: The only way to know your favorite flavor of ice cream is to try every flavor in the store. And while I do not think you need to try every possible tube, I do believe you need to try at least a few in order to learn what you like and what you do not like. With this experience under your belt, the reviews and impressions of others will be much more useful in helping you to decide which tubes to buy.

All this said, I think I can help a little....

First, the essential sound of a 6BL7 is different than that of a 6AS7. So for example, an RCA 6AS7G sounds significantly different than an RCA 6BL7. For those with no experience with the 6BL7, I would encourage you to read this review in Tweak Fi, especially the section on Tube Rolling. Like that reviewer, I notice that the 6BL7 appears be more resolving and also more musical. And I think the sound stage seems to be a bit narrower, and as a result, imaging seems a little less precise to my mind...

http://www.tweak-fi.com/apps/blog/s...nce-system-part-2-glenn-s-headphone-amplifier

Once you have a feel for the sound of a 6BL7, then you can focus on the differences within the 6BL7 family. Sylvania, Tung-Sol, GE, RCA and Japanese-made tubes all sound different. At this time, I am just beginning to explore this family, so I can't comment on the sound of all or even most of these brands.

I currently have the early 1950's flat-plate Sylvanias. These tubes are somewhat recessed in the mids and have what one reviewer describes as a slightly nasally sound. From there, I jumped ship and tried a quad of late 1950's/early 1960's Sylvania 6BX7GT. Electrically, the 6BX7 is very similar to the 6BL7, with the major difference being a lower mu, or amplification factor, 10 versus 15. The mid-range on the Sylvania 6BX7GT seems more natural and I also notice that room reflections and mid-range harmonics are a bit more pronounced, providing rather delicate midrange detail that I quite like. Going back to the 6BL7 family, I have a quad of late 1950's/early 1960's Sylvania 6BL7 with the "X-shaped cross-section" plates enroute. And in the future, I plan to explore other brands within these two tube families.

Other than the Glenn, my system is rather mid-fi. I use an Audio-gd Fun (pre-amp/headamp) as a DAC and my source is streaming Google Music. My headphones are modded Senn 700's (per Takato except for the backwave bass damping mod).

Before I began to roll 6BL7/6BX7, a pair of GEC 6AS7G and a Mullard ECC31 were spending the most time in my amp. With the early Sylvania 6BL7s, the Mullard was a bit too laid back, and I found myself preferring brighter drivers, such as the GEC B36, Philips FDD20 and Siemens C3g. When I rolled in the 6BX7s, the C3g were already installed, and I haven't felt any desire to swap them out, so I can't comment on how this tube sounds with other drivers.

One more observation... With a Glenn OTL, it is also possible to roll two 6AS7's per channel. So if you get these adapters, you could roll four of your favorite 6AS7/6080. This will enable the amp to drive low-Z cans a bit better, but even high-Z cans such as the Senn 650 will benefit from the increased power and control. Further, you can mix things up a bit. Personally, I like both the GEC and Bendix 6080, but they are different. To my ears, the GEC is airy and detailed, whereas the Bendix seems more neutral with a very solid low end. So why not use one of each per side? And yes, I do intend to try this!

I hope this is useful...

Cheers

 

I have decided not to continue with the purchase of my OTL from Glenn. This is for personal reasons and has nothing to do with the quality of the amplifier or Glenn as a person. He's a great guy to do business with.

Glenn has all the parts I have already bought (listed below) and he might be willing to sell some of them to you:

2 x Jupiter copper foil, paper & wax capacitors (0.47 uF)
1 x Lundahl mains transformer & cover (I forget the specifications)
1 x Lundahl choke & cover (I forget the specifications)
4 x 440 uF ClarityCap film capacitors TC600
1 x Khozmo stereo shunt stepped attenuator (48 steps, Charcroft Naked "Z Foil" load resistors)
1 x Goldpoint switch (double pole, three positions, one deck)
1 x Modushop Slimline enclosure (450 mm x 350 mm x 120 mm)

These are all new and unused

I will also be sending him the following tubes, some of which are NOS, but mostly used but strong (80% +)

15 x C3g (1 x pair Lorenz, the rest Siemens)
14 x Sylvania 6BL7 flat plate (1950 - 1952), some rebranded
1 x pair Tung Sol 7236

He might also be willing to sell you some of these. Probably quickest to contact Glenn at Head-Fi (user name: 2359glenn)

Please don't contact me if you are interested as these parts belong to Glenn, not me.

 

^ Sorry to hear that. That would have been a great build based on the parts and tubes you listed.

 

That means my amp is next!

 

That ain't so bad. I know a guy who bought the BHSE "for a good price" even before he had a pair of stats headphones. The best part? It's still at the dealer's shop cos he doesn't know how to explain the purchase to his wife yet, and he's already buying "better" tubes for it.

 

I'm a little disappointed Nate that I will have to wait longer but I am really happy for you. I'm pretty sure you will enjoy Glenn's OTL amp.

 

@MoatsArt

My OTL amp (code name Darna) will be shipped within couple of days. Glenn had sent me some pics which I would like to share with you . Nevermind the stamped date - Glenn is just being lazy setting his camera right!















All pictures were taken by Glenn.

 

Looked like a lot of flexibility in tube rolling there...very nice! What are some of the possibilities?

 

I will be mainly using it with six 6BL7 output tubes for my HD-800SD. Glenn told me that the amp can also run two or four 6AS7s or two 6336 for low impedance phones.

 

That's pretty cool that you can varies the output to match the HPs by rolling in multiple type of tubes.

 

@lukeap69

Glad to hear that you have your OTL. Thanks for the pictures. I'm also greedy for words. Could you please describe what you're hearing? No need to be too verbose or poetic. I'm particularly interested in how it drives your 32 Ohm PM-2. Are you using 2 x 6AS7G per channel for this task?

I think Glenn is working on mine at the moment. Output impedance is occupying my thoughts. This entails making final tube choices for the cathode followers and asking Glenn to consider switchable bias to optimise the operating points for the tubes that have taken my interest.

I'm not going to be tube rolling. To be honest, it makes me nauseous because of bad experiences I've had. Just want to choose nice tube types for differing purposes.

 

Hi Nate

Are you back or are you back?

TBH, I haven't used my PM-2 much with my Darna - the HD800SD and HD650 get most head times. In my previous adventure of finding the right tube combo for the PM-2, I have decided that the 2 pairs of 6AS7's (Chatham) is the best I have heard my PM-2 on my Darna. I will have to try it later to provide a bit more details on the sound as I have 3 pairs of 6BL7's now rocking (although I think I prefer 3 pairs of 6BX7's instead.) Will get back to you as soon as I can.

Hope you get your OTL amp soon. I have one suggestion though, my amp when using 6BL7's has very high gain. I'm not sure if Glenn can do something to lower the gain a bit or add a gain selector of low and high.

Later.

Arnold