Kegger/blueglow kt88 project

[StepheK]

Stephe,
Have you ever tried running the 6ej7 with g2 as anode? I tried grounding the plate, the g3, and pin6 and put b+ to g2. And I like the results. Less noice I guess. You can hear more of the decay of the notes and space around the instruments.

G2 is rated for 0.9 watts but you can exceed that some. I guess because the anode is not adding heat.
Simple to try. I would like to hear your impressions if you try it.

Thanks

Never even thought of trying that. Applying negative voltage to the plate and positive to the screen, in my mind wouldn't those elements just pass current like a diode as there is no grid to control the flow of electrons? I'll admit I'm baffled how that could even work.

 

[Todddo]

Screen as anode.
Obviously not explaining it well.
Put b+ on the screen (G2) only. This makes G2 the plate effectively.
instead of the normal triode wiring with b+ on the anode and G2 and g3.
Still making it a triode.
I grounded the anode, g3, and pin 6 which is a shield. But they don’t have to be grounded.

Based on the standard kegger voltage and current for the driver stage, the screen dissipation of 0.9 watts is okay.

 

[Defcon99]

Questions about Using different Power Transformer/Rectifier/PSUD2:

Seeking advice on using an older TRIAD R-21A trans w/5u4 rectifier.

TRIAD R21-A specs: 117v, 400-0-400v (200mA), 5v@3A, 6.3v@6A vs. Edcor: 120v, 380-0-380v (200mA), 5v@3A, 6.3v@5A. 5u4g voltage drop 35v vs 5AR4 10v. Choke is a Hammond 193J (10H, 82ohm). Line is 120-121v.

Using PSUD2—BOTH the TRIAD/5u4g, and the Edcor/5AR4 resulted in B+ of around 480v. However, for the first Edcor/5AR4 that I built, B+ ended up around 460v (with the only mod being a CL-80 on the primary.) I don’t understand the 20v difference (PSUD2 480v vs actual of 460v?)

I’m wondering since both simulated out to be 480v, would the final TRIAD/5u4g results also end up to be in the 460v range or will I need an additional RC stage. I’m hoping someone who knows more about PSUD2 could double check my results. Also, I suspect 117v primary with 120-121v line voltage could result in the 5v/6.3v filaments being too high as well.

Also, I seem to recall Mark mentioning the need to recalculate the first cap after the rectifier with the 5u4g (currently 10uf with 5AR4.) Is the 10uf/630v still good with a 5u4g? As mentioned in post #1763 is adding diodes to the 5u4g needed?

Attached is my PSUD2 results with the TRIAD/5u4g, all else the same as well as the original pwr schematic.

Thanks in advance for any and all help.

 

[Hyakuya]

My PT has a 410-0-410 secondary. With a GZ34 and a dropping resistor I get about 455V +B.

I would build it up, add a resistor and measure your +B and filaments then adjust to get what you want. Maybe use a dim bulb tester or a variac if you have one. You can put a high wattage resistor before the first cap or add a RC stage, up to you. Mine is split rail, after the first cap into 2 chokes, second cap.,etc. with a 270R resistor on each channel.

No need to change the first cap and the diodes are optional as a safety precaution more than anything else (I use them).

Can't help with your PSUD questions I'm afraid...

I just switched mine from UL to triode without the feedback (don't have a switch). I think it sounds better !!

 

[opnly bafld]

I just switched mine from UL to triode without the feedback (don't have a switch). I think it sounds better !!

Because I used OPTs already on hand without a UL tap mine is triode only without feedback and I have been very happy with it for almost 3 years. Never heard a UL version so I obviously can't compare the two, so I appreciate the feedback (or no feedback as the case may be ).

 

[opnly bafld]

@Defcon99

More eyes with more experience/knowledge will see your question if you start a new thread.

 

[Defcon99]

My PT has a 410-0-410 secondary. With a GZ34 and a dropping resistor I get about 455V +B.

I would build it up, add a resistor and measure your +B and filaments then adjust to get what you want. Maybe use a dim bulb tester or a variac if you have one. You can put a high wattage resistor before the first cap or add a RC stage, up to you. Mine is split rail, after the first cap into 2 chokes, second cap.,etc. with a 270R resistor on each channel.

No need to change the first cap and the diodes are optional as a safety precaution more than anything else (I use them).

Can't help with your PSUD questions I'm afraid...

I just switched mine from UL to triode without the feedback (don't have a switch). I think it sounds better !

 

[Defcon99]

Very helpful. Thank you. I may try your mod on removing the FB in triode. My hope is that a 5u4g would eliminate the need to use a dropping resistor. But I really need to know how to use PSUD2 to confirm. I may post a new thread to see if someone can help with that. Thanks for your help.

 

[Defcon99]

@Defcon99

More eyes with more experience/knowledge will see your question if you start a new thread.

Good advice. Thanks.

 

[WntrMute2]

Very well done, looks better than mine I think
Stay tuned, I'll make a post on how to tame that Power Transformer hum...

Any progress on a video or info in general of this? I still have a humming PT I can't quiet down. Not overloaded. Bells are nice and tight etc.

 

[StepheK]

Any progress on a video or info in general of this? I still have a humming PT I can't quiet down. Not overloaded. Bells are nice and tight etc.

If it's an Edcor, IMHO the only solution is to replace it with a Hammond unit. You will have to replace it eventually as it's very likely to short out anyway. I know mine did after wasting a bunch of time trying to rubber mount it etc.

 

[WntrMute2]

It is a Heyboer unit. Only one of 4 that's noisy.

 

[nerdorama]

It is a Heyboer unit. Only one of 4 that's noisy.

Have you removed the end bells in case there is anything to see? I had a Stancor power transformer that buzzed quite loudly. I found that the lam stack didn't fill the opening of the coil window. Some composite wedges tightened things and the buzz died.

 

[WntrMute2]

I've had it apart to powder coat the bells and didn't notice anything loose.

 

[Zaemon]

Hey All. Just finished my build and figured I'd share. This thread was definitly very helpful, so thanks to all for sharing their tips and tricks. Its mostly stock to how Mark built his, but a few simple additions.

-Powder coated the chassis and transformer bells.
-Added 1/8" steel plates to the bottom to add more legit feet, and helps a lot to keep the chassis sterdy with the weight of the transformers.
-Bleeder resistors for the power supply caps.
-Jupiter caps for everything within the audio path.
-I added StepheK's "tube headphone box" cicurit, but built it within the chassis as oppose to a seperate enclosure. Speaker or headphone output can be selected via the back with a DPDT switch. Its a very easy to add feature and sounds great. Big thanks to StepheK as well. Her youtube channel/website is truely an amazing resource of knoweldge.

Only minor issue like many have seemed to experience here is some hum from the Edcore PT. I bought there silicon mounting pad hoping that would help, but its still a bit noticeable. Luckily, its not really present in the audio signal, just kind of distracting when around the amp. I may try and troubleshoot that later, but for now its not bugging me enough to not enjoy the amp.

Thanks to Mark as well for helping create such a fun and approoachable project.

Cool stuff. Exactly what im gonna build too.
Read through this whole threat with all its ups and downs, a well of knowledge and top notch builds. Great stuff.

 

[Lavane]

Any progress on a video or info in general of this? I still have a humming PT I can't quiet down. Not overloaded. Bells are nice and tight etc.

Ive stuffed folded pieces of cardboard between the end bells and winding before that helped quietning a transformer.

 

[Blueglow]

Congrats on the build. You can always redip the transformer windings and see if it helps. I've done that with success.

 

[Remy K]

I just switched mine from UL to triode without the feedback

I found that mine in triode mode had poor bass control, so I switched back to UL. Sounds cleaner with tighter bass.

 

[opnly bafld]

Hopefully we find what works best for us in our system and room.

My triode strapped amplifier works well for me.

 

[zackthedog]

Here's my entry in the Blueglow sweepstakes. My daughter, who just graduated from college, has been wanting to build a tube amp for some time now, and asked if maybe we could do something when she drove down from Seattle for Christmas week. I thought a Blueglow amp would be an easy project for a beginner (with help). I've been sort of curious about it for a while myself. I dug through the shed and came up with parts from my old SE 300B amps. An Angela Universal power tranny, two James 6123 output transformers, and a Hammond chassis I ordered for a project that can wait. I ordered a 10H/200mA choke, some tubes and some extra passive parts, and did some spray painting. Meanwhile she watched all of the YouTube videos before she came down. We only had five days so we kind of had to improvise at some points, and while she did a lot of the soldering etc., last night I had to take over for the final wiring while she observed, just to speed things along. But she did get a chance to understand how tube amps work, how this particular circuit worked and generally how to lay things out and put it all together. It turned out much better than I expected. I was able to squeeze in some measurements this morning before she headed back north. And yes, I added a knob to the volume pot and managed to toss the bottom plate and some feet on. ;-)




The performance is remarkably good! The 10kHz square wave is a little lumpy but that's true of every Japanese OPT I've worked with so far. They seem to have a zingy top end. But since there's no global feedback I'm not worried about it. It sounds great. I was especially impressed with the THD--1% at 12 watts. And that's using the 3.5K plate tap. Flat from 20Hz-20kHz. No wonder it sounds so good! It's also very quiet. I dispensed with the triode/UL switch--I don't like them and she needs all the power she can get, so we just wired them for UL. She was amazed at the sound and spent the evening listening to it on my system. She has an all-in-one turntable at home, a decent one I bought her last Christmas. I gave her some nice little Andrew Jones Pioneer bookshelf speakers I bought a few years ago, so she'll have a complete system now.