A few questions for my Simple SE

[Salsero]

I am building a simple SE using KT88 tubes with a choke supply - a few questions follow:
1. What value should I use for the R17 and R27 resistors?
2. I am going to use a socket with a filter and fuse - what AC line power rating should I specify?
3. There are several switches used for the amp - the standby, ultralinear and cathode feedback switch. Any recommendations on which switches to select?

Thanks all
Salsero

[spacemen12]

Originally Posted by Salsero

3. There are several switches used for the amp - the standby, ultralinear and cathode feedback switch. Any recommendations on which switches to select?

Not the standby switch.
From Simple SE :
"The assembly instructions for the Simple SE show the optional installation of a standby switch. There have been a few instances of blown diodes associated with the use of a standby switch. Investigation has revealed that some power transformers (particularly Hammonds) can generate a 2500 volt spike when the standby switch is operated. It is recommended that the standby switch be omitted from new builds, and not used on existing amps. The instructions will be changed as soon as I can get to it."

[SGregory]

Salsero,
What is the power transformer you will be using and the DCR of the choke and the impedane of your OPT's. To determine the value of the resistors optimally you need to estimate your plate voltage. Using the table in the assembly manual we can then determine the resistor value based on how hard you want to drive your tubes.

For Example, in mine I use the EDCOR XPWR033 which will get me close to 450VB+ with 150OHM DCR on my choke. I used 560Ohms for R17/27.

The only switches I use is the Power and sometimes the CFB. I run CFB almost all the time. I do have the UltraLinear switch installed but don't care for the sound (personal preference). I am also driving 4ohm speakers with little transformers. UL sounds whizzy to me.

I am using a 1.5amp sloblo fuse. No thermistor.

[Nikon1975]

George,

The boards arrived, thank you very much ! I have a couple of questions:

1) For the simpleSe, my transformer does not have a 6.3V 5A secondary, but two 6.3V 3A. Can I connect them in parallel in the board socket ?

2) I saw in the schematic of the PSU of the SimpleSE that you do something that I would like to understand, connecting the B+ to the heater. What's the theory behind that ?

3) Did I understand correctly that the SimpleSE uses hybrid rectification ? What are the advantages and disadvantages of this approach ?

Thanks,

Davide

[Salsero]

I have not found the heat sinks for the CCS. I tried Mouser and Digikey. Maybe I am just missing it. Anyone, please let me know what current part number and source to look for? Furthermore, after reading the heat sink requirements for the CCS, should I try to get a bigger heat sink than the one described in the Tubelab parts section?

Thanks
Salsero

[Ty_Bower]

I used the 532-530714B00 heatsink from Mouser. You might also want to include its mounting kit, 532-4880SG.

I'd encourage the use of a slightly larger heatsink if you can be sure you will have enough space to mount it. These little heatsinks will work fine with a 12AT7, but I have some other substitutes that like to draw a lot of current. This makes the CCS need to dump a lot of voltage to keep the current at spec and the heatsinks can run hot.

[oldngray]

Do the heatsink and transistor actually need to be screwed to the PCB? If you build the inverted configuration why not use a larger heatsink and install them on an angle say at 45 degrees?

[rknize]

As long as the heat sink is attached to the chassis somehow, you can do whatever you want. You don't want to depend on the IC leads to be the only mechanical support for a heavy heat sink.

[oldngray]

I've read through the Simple SE instructions but I'm not clear on how we determine B+ voltage.

This is my 1st build so I'm going with the default configuration. But the parts list states that you might need to make changes to R17/27 and C1/C2 depending on your build. Where did I miss the instructions for calculating these new values?

The current plan is to use the Edcore XPWR059 power transformer 750V (375-0-375) and the following tubes: JJ6L6GC outputs, JJGZ34/5AR4 rectifier and JJ ECC81 as my 12AT7 equivalent. I thought the B+ for this combination is 450 so going to the 'tubes and transformers' page do I get
6L6GC 450 5000 437 37 560 66 27 3.95 .... 3.95 Watts for my power output?

Per the table instructions, I'm not sure how to get a B+ value based upon my transformer.

Lastly, can someone recommend a DPDT rotary switch suitable for use for the Triode/UL control and CFB selector?

I also plan to include the choke and the power supply cap. those additions don't appear to impact any on board components, right?

thanks!

[tubelab.com]

Do the heatsink and transistor actually need to be screwed to the PCB?

No, but the heatsink is connected to a high voltage. Make sure it doesn't touch anything.

I'm not sure how to get a B+ value based upon my transformer.

There are many variables in the transformer to B+ voltage formula, and some can not be easilly answered. The hard ones are how much is your line voltage, how distorted is it, and does the transformer really meet its specs. The usual rule of thumb is secondary voltage * 1.2 to 1.3 for a tube rectifier. That gets you somewhere near 450 volts.

3.95 Watts for my power output?

4 watts for a 6L6Gc in triode mode is a bit conservative but you won't get much more than 4.5 to 5. UL mode can get you 8 or 9 watts. A KT88 will do about 7 or 8 in triode and 13 to 14 in UL.

I also plan to include the choke and the power supply cap. those additions don't appear to impact any on board components, right?

You leave out the 150 ohm 5 watt resistor if you are using the choke.