Thanks gotan. I do not plan on modifying the amp. I will just figure out which tubes I like best and stick with that.
Oh, I will! I still have to do an inventory of parts (the transformers are there, that's good!), but then my new soldering station is ready.
Hi, Victor, I already have two questions, and I am going to ask them here, because I think the answers might be of interest also to other builders of the kit.
1a) Can I mount the power transformer and the Lindahl transformers on rubber grommets, to mechanically/vibrationally isolate them from the chassis, or is there not enough headroom for that? (Obviously I will be able to figure that out myself once I do a dry fit, but maybe there are other reasons one might not want to do that that I'm not aware of.)
1b) I assume the mounting screw chassis ground connection is important for all three transformers just for safety reasons. So if using rubber grommets I would need to make sure to maintain that electrical contact to the chassis. Correct?
2a) Should I swap out the kit AC cable for a standard US three prong AC cable?
There is a flying ground connection on the cable that came with my kit, but the outlets at our place do not have an extra grounding screw. From both the schematic and the PC board layout it looks like the grounding conductor is connected to the chassis, and expects a safety ground connection.
I assume the TU-8200R must be operated with a chassis ground connection, since the chassis is metal.
As I already knew from other posts here and elsewhere, this looks like a really nice kit. I'm positively surprised by the weight of the chassis. Our cats will have a very hard time pushing it off the table.
1a) Can I mount the power transformer and the Lindahl transformers on rubber grommets, to mechanically/vibrationally isolate them from the chassis, or is there not enough headroom for that? (Obviously I will be able to figure that out myself once I do a dry fit, but maybe there are other reasons one might not want to do that that I'm not aware of.)
1b) I assume the mounting screw chassis ground connection is important for all three transformers just for safety reasons. So if using rubber grommets I would need to make sure to maintain that electrical contact to the chassis. Correct?
2a) Should I swap out the kit AC cable for a standard US three prong AC cable?
There is a flying ground connection on the cable that came with my kit, but the outlets at our place do not have an extra grounding screw. From both the schematic and the PC board layout it looks like the grounding conductor is connected to the chassis, and expects a safety ground connection.
I assume the TU-8200R must be operated with a chassis ground connection, since the chassis is metal.
As I already knew from other posts here and elsewhere, this looks like a really nice kit. I'm positively surprised by the weight of the chassis. Our cats will have a very hard time pushing it off the table.
And a few other questions, not just to Victor:
I see the time constant of the bias auto adjust has been changed from 0.22s to 0.33s between TU-8200 and TU-8200R, and the bias overcurrent sensing opamps and bias overcurrent protection optoisolators have been removed. There was a comment from Ferenc that by the time the overcurrent protection in the TU-8200 would kick in the bias unit FETs would be cooked anyways. Has this change been discussed somewhere already? If not, would anybody (maybe Ferenc?) care to comment?
R59 and R60 have been changed from 22k to 100 kOhm, and a lot of the various supply/bias voltages have been slightly changed (increased), including the DC heater voltages. It seems the nominal voltage at the heater rectifier bridge output has also gone up. Does that mean the AC heater voltage for the 6L6GT power tubes has also been increased?
I have no reason to doubt that the TU-8200R is an improvement to the TU-8200, so please don't misunderstand these questions as anything but an expression of my curiosity. If these changes have already been discussed elsewhere, please be so kind and point me to it.
I see the time constant of the bias auto adjust has been changed from 0.22s to 0.33s between TU-8200 and TU-8200R, and the bias overcurrent sensing opamps and bias overcurrent protection optoisolators have been removed. There was a comment from Ferenc that by the time the overcurrent protection in the TU-8200 would kick in the bias unit FETs would be cooked anyways. Has this change been discussed somewhere already? If not, would anybody (maybe Ferenc?) care to comment?
R59 and R60 have been changed from 22k to 100 kOhm, and a lot of the various supply/bias voltages have been slightly changed (increased), including the DC heater voltages. It seems the nominal voltage at the heater rectifier bridge output has also gone up. Does that mean the AC heater voltage for the 6L6GT power tubes has also been increased?
I have no reason to doubt that the TU-8200R is an improvement to the TU-8200, so please don't misunderstand these questions as anything but an expression of my curiosity. If these changes have already been discussed elsewhere, please be so kind and point me to it.
I hope you follow the maunal step by step to build your amp kit.
I want you have a succesful story..
After your amp is working, you can do your way...
I want you have a succesful story..
After your amp is working, you can do your way...
Ferenc, re-reading this thread I saw you announce you would post a comparison of the TU-8200R to the original TU-8200. I assume you got completely bogged down with answering individual questions, so you never got around to posting that comparison. If you still have your notes, I would be very interested in seeing your comments on the changes to the R version.
Just discovered I now can send PM's!
Just discovered I now can send PM's!
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And it works! Victor, there is an extra yellow wire with a connector already crimped on coming from the primary side of the power transformer. The instructions do mot seem to mention it. Is that a shield or grounding connection that should go to board ground or the chassis? For now I coiled it up, and left it on top of the transformer.
As I remember my European version (230V) do not have this "extra"/standalone wire.
But you said the amp works well. Nice job! What is your first impression about the sound of this amp?
But you said the amp works well. Nice job! What is your first impression about the sound of this amp?
Thanks for the info about your power transformer. Maybe there was an update to the transformer; my understanding is that the kit should be the same for 240V and 120V AC countries, since the 'unit-8' circuit board has socket positions labeled 230V and 115V.
Regarding the sound, my first impression is that I'm enjoying listening to this amplifier.
I have listened now for a few hours, mostly through headphones (Sennheiser HD6xx, open back, 300 Ohm), but also through speakers (KEF R3, 8 Ohm, minimum impedance 3 Ohm). I have the amp set to ultra linear mode, high speaker impedance, and the headphone output to low.
I think it's fair to say I'm probably not your typical tube amp aficionado. I bought the TU-8200R amplifier kit because reading online reviews it seemed like it might be a good (competently designed, pleasant sounding, not obviously flawed as an amplifier) example of single ended tube amplifiers. I am curious about their sound, and whether they are really significantly different from neutral amplifiers. Obviously I was also excited about assembling an amplifier myself.
From what I heard so far, I'd say that if there is some (positive or negative) SET-typical distortion, it's not right in your face at the relatively low volume levels I'm listening at.
Regarding the sound, my first impression is that I'm enjoying listening to this amplifier.
I have listened now for a few hours, mostly through headphones (Sennheiser HD6xx, open back, 300 Ohm), but also through speakers (KEF R3, 8 Ohm, minimum impedance 3 Ohm). I have the amp set to ultra linear mode, high speaker impedance, and the headphone output to low.
I think it's fair to say I'm probably not your typical tube amp aficionado. I bought the TU-8200R amplifier kit because reading online reviews it seemed like it might be a good (competently designed, pleasant sounding, not obviously flawed as an amplifier) example of single ended tube amplifiers. I am curious about their sound, and whether they are really significantly different from neutral amplifiers. Obviously I was also excited about assembling an amplifier myself.
From what I heard so far, I'd say that if there is some (positive or negative) SET-typical distortion, it's not right in your face at the relatively low volume levels I'm listening at.
My amp seems to be running at about 50C (120F) chassis temperature, i.e. it's pretty warm but not too hot to touch. Is that expected? What do other owners observe?
When I used 6L6GC and 6550 tubes the chassis was warm, bit not too warm, I think as by you.
I think the main heat came from tubes and the tubes warming up the chassis (not the transformer or inner parts).
Since I use 807 tubes the chassis is just "light" warm. Adapters+the height of 807 tubes give the situation where the tubes are over the chassis so they don't warm up the cover.
I think the main heat came from tubes and the tubes warming up the chassis (not the transformer or inner parts).
Since I use 807 tubes the chassis is just "light" warm. Adapters+the height of 807 tubes give the situation where the tubes are over the chassis so they don't warm up the cover.
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Actually, I was wrong with my temperature estimate. I now measured the temperature, and it is only 35C, 10C above ambient, so nothing to worry about. This is while the amp is drawing 63W from the 120V mains.
A thermal picture after a few hours of running. The case above the main PC board is at 47C, still not excessive:
So, turns out that wire is really needed. Something must have hit the connector housing, and on closer inspection one can see that half of the 7th pin position broke away (*). That's where that yellow wire is supposed to go.
The amp seemed to run fine, but the idea that there would be an extra wire from the transformer just didn't sit right with me, so I opened it up and measured the test point voltages. They were all 18% low, starting right at the rectifier bridges. (My AC is right on at 119.5 V at the fuse.) Victor confirmed that the yellow wire needs to be connected (super fast reply as always!), so I repaired the crimped-on pin insert, and plugged it into the unit-8 receptacle, together with the other 5 pins still seated in the connector housing.
All voltages are now within range:
| TP | value | value | range |
| 1,2 | 3.42 | 3.425 | 32 - 3.7 |
| 3,4 | 3.326 | 3.446 | 3.2-3.7 |
| 5,6 | 113.6 | 114.2 | 100-120 |
| 7,8 | 116.1 | 112.6 | 100-120 |
| 9,10 | 206.2 | 208.4 | 195-220 |
| 11,12 | 1.087 | 1.088 | 1.0-1.2 |
| 13,14 | -17.93 | -18.00 | -12 - -24 |
| 15,16 | 278.5 | 278.5 | 265-290 |
| 17,18 | 0.446 | 0.443 | 0.4-0.55 |
| 19,20 | 270.4 | 270.6 | 255-280 |
| 21,22 | 264.4 | 264.8 | 250-275 |
| 23,24 | 277.5 | 277.3 | 255-280 |
| 25 | 292.8 | 270-300 | |
| 26 | -32.78 | -29 - -35 | |
| 27 | -34.02 | -30 - -36 | |
| 28 | 6.16 | 5.6-6.4 | |
| 29 | 6.46 | 6.0-6.8 |
(*):And I just checked the box the amp kit came in: the broken off part of the connector housing was still in there below all the packaging I kept. Victor says this is the first time this has happened. Good thing nothing burned up. I was a bit worried when I saw the low heater voltages, since supposedly that is not good for tubes.
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And I'm really glad that I didn't follow through on my idea of grounding that extra wire. Best case, it would have blown the fuse or circuit breaker. Worst case, it could have fried anything in the amp connected to ground (which is pretty much everything), or the person touching the 'on' switch.
Any amplifier can last you a lifetime, if you use it right.....
Any amplifier can last you a lifetime, if you use it right.....