New SET

[Ruidoso Bill]

Really new Guy Trying to Build.

Built my first ever amp, a SET KT88, followed Blueglow on YouTube,

Couple of questions, first one, KT88 internal glows less bright than the the other. Amp sounds amazing, had assembly issues crimped wire on PS Transformer to chassis, second actually had a short with broken chassis ground shorted on neutral thermistor lead, didn't see it until the end. Amp sounds wonderful, clean, clear and precise. Question one is is it acceptable for one of the KT88 to glow brighter than the other, second question is does a GZ34 have a little hum when at full power?

Thanks for the dumb questions.

 

[Bigun]

How are the heaters wired up? I”m unfamiliar with the KT88 but I could imagine they are designed for parallel not series wired heaters.

 

[Tjj226]

Really new Guy Trying to Build.

Built my first ever amp, a SET KT88, followed Blueglow on YouTube,

Couple of questions, first one, KT88 internal glows less bright than the the other. Amp sounds amazing, had assembly issues crimped wire on PS Transformer to chassis, second actually had a short with broken chassis ground shorted on neutral thermistor lead, didn't see it until the end. Amp sounds wonderful, clean, clear and precise. Question one is is it acceptable for one of the KT88 to glow brighter than the other, second question is does a GZ34 have a little hum when at full power?

Thanks for the dumb questions.

No and no.

You miswired your heaters, and a gz34 shouldn't hum at all. Do you have a volt meter to check all the voltages?

 

[Ruidoso Bill]

Heaters are wired in Parallel, Amp sounds great. Here are some pics

 

[Diabolical Artificer]

Is the GZ34 referenced one side to ground or center tapped? Htr wire looks a bit too small on the OP valves; is it solid or stranded?

Check each KT88's htr resistance, check voltages, if there's still a problem try popping in a sense resistor of an ohm or less to check the current.


Andy.

 

[Parafeed813]

The heater filaments of the brighter valve probably just extend a bit from the cathode sleeve.
Nothing to worry about.
Swap the two KT88s to check that it is not something caused by the amp.

 

[Alan4411]

... Couple of questions, first one, KT88 internal glows less bright than the the other. ... is is it acceptable for one of the KT88 to glow brighter than the other, second question is does a GZ34 have a little hum when at full power?

First 'test' is to swap the two KT88s round.
If the one that is brighter is still brighter in the other position and the dimmer one still dimmer in the other position that is probably down to the heater/cathode assembly inside the tubes. Ignore it.
But, if the brighter one becomes the dimmer one if you swap them round (and vice versa) you have extra resistance in the dimmer location's wiring. That could be marginal wire thickness or a poor solder joint etc.

The GZ34 itself should not hum? Can you explain? Do you hear a hum from the speakers 'at full power' or from the transformer perhaps?
By the way, it looks correctly wired in your picture. Do not reference the GZ34 heater winding ''to ground'', or you get a bang...

 

[Ruidoso Bill]

New Set

Swapped the tubes and the bright tube moved so that's a relief, heater wiring is 18 ga slilver plated stranded PTFE. I noticed the hum when I had it upside down on the bench, possibly the transformer, nothing through the speakers. Should I consider buying additional KT88's, Thanks for the info Alan, very much appreciated.

 

[Alan4411]

All good then.

... Should I consider buying additional KT88's,

There is no reason to.

 

[Ruidoso Bill]

Thank you, this amp sounds amazing.

 

[Chris Hornbeck]

Beautiful construction. It's always a pleasure to see real craftsmanship. Thanks.


All good fortune,
Chris

 

[Ruidoso Bill]

Thanks Chris, appreciate your comment.

 

[lavane]

Nice clean layout. If the power transformer is making a bit of noise try tightening the bell cover screws and mounting screws. Also adding some rubber washers on the mounting bolts between the transformer and chassis can help with mechanical hum.

 

[Ruidoso Bill]

Great suggestion of rubber washers, I would never have thought a transformer would make any noise/vibration, this may be my common practice for the next build! I did replace the bell cover screws so I could have acorn nuts for better appearance, I love listening to music but have discovered building is as much or even more enjoyable. Really want to build a preamp next.

 

[Ruidoso Bill]

I was thinking about building one more KT88 Set with some changes. I contacted Hammond Mfg about getting a chassis 17 X 10 X 3 in primer, no powder coat, not easy and they want 10 minimum, does anyone know of another mfg that I can get a steel chassis in primer or unpainted, no powdercoat?