Tubelab SE build and power supply questions.

[Binaural]

Ok, well I'm well on my way getting this thing built. I figured that I'd post my questions here as I know George is a busy guy, and I'd like to get others input as well. I have done a search for these topics, but haven't found answers to my particular questions.

I have constructed the board with all components on the bottom so I can mount the board to a chassis with only the tubes coming through the surface. The only problem is mounting the semiconductors. Not really sure the best way of approaching this. Is it ok to mount the front side to the heat sink to keep the orientation of the heat sinks the same or would this not work? Do the heat sinks have to be attached to the board? I see no traces going to or from the board connections for them.

Secondly, I will be using 300B's with this board and am shooting for a B+ of as close to 400V as I possibly can get. George states at his site that C4 and R4 are responsible for setting the B+, the higher the value of C4 and the lower the value of R4 will raise the B+. For the power transformer I'll be using either the 273 or 373CZ with a 5AR4. I might use a choke and replace R4, but only if hum becomes an issue.

Finally, I'll need to have balanced inputs for the amp to interface with my balanced studio gear. I will use some kind of Edcor transformer. Not sure what secondary impedance to use, but my studio gear runs at 600 ohms. Will there need to be any modifications to the existing circuitry to interface with a transformer? Also I could not find in the assembly manual anywhere how to connect the inputs. There are 10 pads at the front of the board where the inputs/volume control go, but not sure how to wire them. Also I will not be using a volume pot, will I need to solder a resistor in it's place or just a jumper?

Looking forward to your responses. I'm going to play in the snow YAY!

Thanks,
Joe

[Evenharmonics]

Originally posted by Binaural
Is it ok to mount the front side to the heat sink to keep the orientation of the heat sinks the same or would this not work? Do the heat sinks have to be attached to the board? I see no traces going to or from the board connections for them.

Which face of heat sink shouldn't matter as long as it is attached securely to it. The reason for board mount is to keep it from moving which can damage those tiny transistor leads.

Secondly, I will be using 300B's with this board and am shooting for a B+ of as close to 400V as I possibly can get. George states at his site that C4 and R4 are responsible for setting the B+, the higher the value of C4 and the lower the value of R4 will raise the B+.

You want 350 to 370V for B+ since most 300B tubes have 400V max rating.

Finally, I'll need to have balanced inputs for the amp to interface with my balanced studio gear. I will use some kind of Edcor transformer. Not sure what secondary impedance to use, but my studio gear runs at 600 ohms. Will there need to be any modifications to the existing circuitry to interface with a transformer?

I would just build a pair of interconnect cables with balanced plug one end and RCA plug at the other end (amp). As far as I know, this board is ready to accept 2.5K - 5K Ohm primary OPT.

Also I could not find in the assembly manual anywhere how to connect the inputs. There are 10 pads at the front of the board where the inputs/volume control go, but not sure how to wire them. Also I will not be using a volume pot, will I need to solder a resistor in it's place or just a jumper?

R1 and L1 are for input ground lead, R2 and L2 are for input signal leads. You can leave the rest untouched. You may need a resistor at R2 & L2 in series if the noise / hiss level is an issue but if you do, why not just use a volume pot for flexibility.

[Evenharmonics]

Originally posted by Binaural
For the power transformer I'll be using either the 273 or 373CZ with a 5AR4. I might use a choke and replace R4, but only if hum becomes an issue.

There have been many posts here about the buzzing problem with Hammond PT. Apparently, their quality is not what they used to be anymore. I would try Edcor instead. While ago I contacted Edcor for a PT that works for this amp and here's a quote I've got.
"For a 325-0-325 200mA, 6.3v 4A, 5v 2A would cost $60.42 each plus a one time design and setup charge of $20.00 plus shipping charges. Lead time 6 weeks."
That's about the same price as Hammond PT suitable for this amp.

[Binaural]

Evenharmonics,

Thanks for your reply. As far as the heatsinks, i was thinking this was the case, but I wanted to double check as I haven't done it this way before and wanted to avoid that horrible smoke that I see way too often!

I read on George's site that he prefers to run the B+ a bit higher (but under the max, rare for him... haha) and use a OPT with a higer primary impedence (5k) for better bass control with about the same amount of power.

I might not have described what I want to do with the input transformer as well as I could, since you are talking about the OPT primary. What i'm talking about doing is connecting an input transformer to the input of the board. Nothing to do with the output transformer. I was asking what the input impedance of the input section of the board is, so I know what secondary i would need. This would assure a balanced connection from the output of my monitor controller to the amp, and also assure a consistent 600 ohm connection thorough out. (plus I love the sound of transformers, so that would be an added bonus.)

Adding a volume pot on the input would be redundant and unnecessary, plus i've never been a fan of carbon pots. If i put anything there, it would be a stepped attenuator for more precise control, but as stated, this would be unneeded.

That's sad to hear about the Hammond Xformers. I have an Allied 6K56VG in use in my Aikido phono stage and have had no problems with it and I thought they were made by Hammond. I will check out the Edcor as I love their transformers anyways. I was going to use one of theirs on the input. Sad none of their standard models has a 5V winding for the rectifier filament.

[Evenharmonics]

Originally posted by Binaural
I was asking what the input impedance of the input section of the board is, so I know what secondary i would need. This would assure a balanced connection from the output of my monitor controller to the amp, and also assure a consistent 600 ohm connection thorough out. (plus I love the sound of transformers, so that would be an added bonus.)

As for the balanced versus unbalanced connections, the way I see it and have been told is that people choose SET tube amp such as Tubelab SE, despite its low power output, for its sonic signature (even harmonic distortion). People would compensate for its low power by using high efficiency speakers which makes it challenging to solve noise floor issues but they go through all that effort to experience its sonic signature. Using balanced line level circuit will add odd harmonic distortion which defeats the purpose of choosing this type of amp.

I do not know the input impedance in numbers for Tubelab SE but I have tried it with studio gears via unbalanced connection and it works fine for home use.

[Binaural]

Hmm, sounds very strange. Never heard of that before, but then again, that department is quite large. Thanks for your help EH.

[Evenharmonics]

Here is a bit of info on even and odd harmonic distortions and what they do.

[mpilley22]

hello i just populated my tubelab se board im running 300b's and i cant for the life of me figure out what wires go were on the power transformer t1 1-8 my power transformers 660v hayboer my outputs are hayboer to i dont want to do this wrong please help i emailed george anderson 15 times no responce
my power transformer will arrive monday

[Evenharmonics]

Originally posted by mpilley22
hello i just populated my tubelab se board im running 300b's and i cant for the life of me figure out what wires go were on the power transformer t1 1-8 my power transformers 660v hayboer my outputs are hayboer to i dont want to do this wrong please help i emailed george anderson 15 times no responce

He is very busy from what I've been hearing lately. I'm sure he would respond if he can.
Is there a diagram for your new power transformer? This thread may help if their wiring use same color code.

[tubelab.com]

help i emailed george anderson 15 times no responce

I only counted 5

He is very busy from what I've been hearing lately. I'm sure he would respond if he can.

I work for a company that has laid off 100,000+ people in the past 5 years. I have been at work late (often 8PM) 5 or 6 days a week trying to keep my job. Easter weekend, I went out of town to see my mom with no computer access. I responded to the transformer wiring request last weekend, and resent the email again early this morning. Here it is again in case it didn't get there:

Mike,
Sorry for the slow reply. I have been chained to my desk at work lately and Tubelab email is forbidden from work.

I don't know whose transformers that you are using, so I will assume that it uses the standard wire colors. The transformer should have 4 windings that are needed for this amp. It may have more but they can be ignored.

Primary. The primary wires are usually black, If the transformer is intended for 120 volt use it will have 2 wires. These will go to the power switch and the fuse holder. If the transformer has 4 or more primary (black with other color stripes) it was made for multiple supply voltages and must be wired according to the manufacturers recommendation.

High Voltage (660 VCT) secondary. There should be 3 wires. Two are usually red, and the third is usually red with a yellow or black stripe. The striped wire is the center tap and is connected to the T1-1 terminal. One red wire is connected to the T1-4 terminal and one red wire is connected to the T1-5 terminal. It does not matter which red wire goes to which terminal. If your transformer doesn't have these colors you must use the manufacturers data to find out which wires are the high voltage secondary winding.

Rectifier filament winding (5 volt). These wires are usually yellow. There may be a center tap which is usually yellow with a black or green stripe. The center tap is not used on this amplifier and must not be connected to anything. The yellow wires go to the T1-2 and T1-3 terminals.

Main (6.3 volt) filament winding. These wires are usually green. The center tap will have a stripe which is usually black. The center tap goes to T1-6. The green wires go to T1-7 and T1-8. If you are using 300B tubes the center tap is not required. It can be connected to the board or taped up and not used.

Some transformers have a bias tap or additional filament windings. These are not used and must not be connected to anything. Some transformers have a shield or ground wire. It should be connected to the ground lug on the power connector. This is a thin grey wire on an Allied transformer.

George