Vintage amp restoration and Beyond

[karpathion]

Fuuuuuuuuck! 150W amp with 2 power tubes? They go much bigger on these tubes, we won't be able to use them. Still doesn't mean I don't want a set, though.

[GoldenVulture]

Fuuuuuuuuck! 150W amp with 2 power tubes? They go much bigger on these tubes, we won't be able to use them. Still doesn't mean I don't want a set, though.

No no no no no !

A pair of KT150’s can allow an amplifier with a power output approaching 300 watts to be built.

Which is fucking nuts. :old:  They must be like transmitting valves.

[GoldenVulture]

Speaking of nuts, I was just going over the Power transformer and it's taps.

Primary being fed 240v [analog meter] 236 [digital]

The secondaries are written on the transformer as 260v and 130v. In the circuit I've got it gives them as 235v and 125v. Measurement says 265v and 133v.
Circuit says H.T.1 should be 648v, reads at a crazy780v in standby [ which is right at the voltage limit of the caps across it] and 750v full on.
H.T.2 should be 342v before it gets split off to various places, it's reading 400v.

I'll get the new stuff and measure it all again

[karpathion]

Speaking of nuts, I was just going over the Power transformer and it's taps.

Primary being fed 240v [analog meter] 236 [digital]

The secondaries are written on the transformer as 260v and 130v. In the circuit I've got it gives them as 235v and 125v. Measurement says 265v and 133v.
Circuit says H.T.1 should be 648v, reads at a crazy780v in standby [ which is right at the voltage limit of the caps across it] and 750v full on.
H.T.2 should be 342v before it gets split off to various places, it's reading 400v.

I'll get the new stuff and measure it all again

I know that the no load voltages will be a little higher, but you have it loaded and operating. I have a hard time believing that the PT is failing, but surely power caps wouldn't cause that, would they?

[GoldenVulture]

I know that the no load voltages will be a little higher, but you have it loaded and operating. I have a hard time believing that the PT is failing, but surely power caps wouldn't cause that, would they?

More likely the caps. They will bump up the voltage but usually not to that degree.  [100v+ ?]
The transformer seems quite ok but the 130v tap [ac] was wavering by about 3v and the 165v was constant.
There's no model type on either transformer just the brand name and a pinout of the secondary taps on the O.P.T.
The P.T. has the taps labelled at the taps. I'm wondering if I've nailed the right mode ampl. There weren't many with the sliders and of that range a 100W, 120W and 150Watt version as far as I can ascertain. I'm wondering whether this may be the 150w one.
Most of the slider control amps were P.A's.
I think the heater tap read 6.5v

[karpathion]

You get anything figured out yet?

[GoldenVulture]

Waiting for the new caps to arrive, maybe today.

[GoldenVulture]

No caps today , looks like I'll have to wait till monday at least.

[GoldenVulture]

FMD  I got the caps today. I should've payed closer attention to the item description.
The pic they had was wrong. It is for a 250uf cap [69mm x 35mm] with eyelet terminals.

I presumed a wrong picture but the item would be the same/similar dimensions etc.
What I got was PCB mount  caps [43mm x 20mm ] about 1/3 the size of the pictured type with
PCB mount terminals. The dimensions were in the item description but I didn't pay attention to it.
I got deceived by the pic. They look like this.

[ almost exact size ]

I'll try them out but I don't think they're going to be able to deliver the power they should.

I also ordered some resistors. They came  as odered in lots of ten Except for one . They were three short.
On the invoice there is a note they will send them when they restock. [ $1 for each ten pack]

I'm back to finding some decent cans now.

[GoldenVulture]

I removed the old cans and fitted the new caps. I concocted a replacement for the multi-cap. This also included new resistors. I had to adjust the bias which was working better after finding a bad connection at the adjust trim.
Proof of concept was the motive behind doing this and it worked. Fuck all noise. I've only given it a short test with a single 12" in a cabinet and running only two ELs4's. It's still running really high HT. It Sounded okay, the tone controls are pretty ineffective, I'll have to work on that.
When I removed the cans I discovered two of them were only 200v ones that should have been 350v ones.

[img][/img]

[img][/img]

[img][/img]