HIWATT 400 - any queries?

Vox and Hiwatt Discussion

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gingertube
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HIWATT 400 - any queries?

Post by gingertube »

Guys,
I do some hobby work tube amp fixes. More now since I turned 60 and went 3 days per week in the electronic design eng. day job.

Last night a guy dropped a Hiwatt 400 to me for a retube and bias set.

If you have queries relating to these amps I have one open on my bench at the moment so now is your big chance.

Feel free to post any questions here and I'll help if I can. Might be slow in responding but should get around to answers sooner or later.

Cheers,
Ian
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xtian
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Re: HIWATT 400 - any queries?

Post by xtian »

Don't hurt yourself, mate!
I build and repair tube amps. http://amps.monkeymatic.com
gingertube
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Re: HIWATT 400 - any queries?

Post by gingertube »

Xtian - I'll be properly careful.

I did my electronics training while working in a major hospital (way back when) - one of the bits of gear I used to fix was a 700W RF Surgical Diathermy with 2000 Volts at 1 Amp on the anodes of the push pull (Class C) transmitter pentode output tubes.

Should be able to safely negotiate the "pissant" 600V or so on the 6 x KT88 outputs for this amp - not to make light of the risk mind you. 600V can kill you just as dead as 2000V.

Plan is to match the 3 parallel KT88 on each side of the push pull (on my AVO MK3), set the bias voltages (1 per side ONLY) to max negative volts and then power up.
When I'm happy with no smoke, do the final bias adjustments.

I do not like the look of the bias adjustment pots. Will fit new ones before proceeding.

Cheers,
Ian
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rp
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Re: HIWATT 400 - any queries?

Post by rp »

Post some pictures. Always fun to see something I'm not likely to see in person.
Stevem
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Re: HIWATT 400 - any queries?

Post by Stevem »

Dropped is operative word as they weigh a whole bunch! Do you folks think about getting a extra bench charge for these Amps and SVTs like I do at times?
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xtian
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Re: HIWATT 400 - any queries?

Post by xtian »

Yeah, Ian, I wasn't talking about the voltage...

Damn, those transformers are monsters. Lift with your knees.
I build and repair tube amps. http://amps.monkeymatic.com
gingertube
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Re: HIWATT 400 - any queries?

Post by gingertube »

A couple of pictures as promised - taken with the phone so not fabtastic resolution/quality.

Notes:
Not easily seen - heatshield on top to reflect output tube heat back to rear.
"Military" style build.
Wire colours to tube sockets: yellow are anode connections, blue are cathode, green are grids.
Cheers,
Ian
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cbass
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Re: HIWATT 400 - any queries?

Post by cbass »

Stevem wrote:Dropped is operative word as they weigh a whole bunch! Do you folks think about getting a extra bench charge for these Amps and SVTs like I do at times?
Nah dude its part of it I've only worked on one svt though :oops: I have a new rule you can't bitch about an amps weight unless your over 80
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drew
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Re: HIWATT 400 - any queries?

Post by drew »

How many hours/days does the owner have to drive into the outback before he gets to someplace where he can crank that thing without someone calling the cops on him?
Bob S
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Re: HIWATT 400 - any queries?

Post by Bob S »

Wow - look at that wiring/layout...
That's how it's done boys & girls.
Mk 3 AVO - melikes much.
I still remember fighting about who got to use the Mk 8 - or the Tektronix 475.
And Ignitron valves with mercury. Fun times.
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xtian
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Re: HIWATT 400 - any queries?

Post by xtian »

That's beautiful. Like NASA would have wired if there were no weight restrictions for space travel.
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rp
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Re: HIWATT 400 - any queries?

Post by rp »

I was thinking if everything people did was done as heedfully as a vintage Hiwatt, the planet would be all right.
dcribbs1412
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Re: HIWATT 400 - any queries?

Post by dcribbs1412 »

What a beautiful monster :shock:
Thanks for posting pics
600V B+ ?
bb5000
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Re: HIWATT 400 - any queries?

Post by bb5000 »

It should have a plate voltage ~700V if it's working as designed...That amp is a wet dream.
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gui_tarzan
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Re: HIWATT 400 - any queries?

Post by gui_tarzan »

cbass wrote:Nah dude its part of it I've only worked on one svt though :oops: I have a new rule you can't bitch about an amps weight unless your over 80
I've re-tubed an SVT and I told the owner he was going to have to do the lifting for me. I would help, but he is young and strong, I'm neither.
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