Custom Slave 200

[Energy]

Hi all!

I'm new here, so this is to introduce myself and show you what I acquired yesterday. I hope you like it, too:

The amp is approximately 1 year older than me. It's a Slave 200, serial no. 1319! Caps and volume pot have date codes 70.34 and 70.24, respectively. I presume the amp was made in late 1970/early 1971. The transformer numbers read "G9433" and "G9489", which means they were made in 1969, according to member Alnico's theory.



(I replaced the ugly poti knob with a chickenhead.)





The former owner told me that the amp was originally used by The Who.
Maybe, maybe not. In fact, there are white markings applied to the tolex:




I checked pics of original Who gear on www.thewho.net:

Ca. January 1973, examples of stencil markings applied directly to amp and cabinet tolex. Amplifier heads were often numbered in the early ’70s as well.

Makes me think the former owner could be right and the amp once actually was part of the Who's equipment.

Anyway, the amp works and sounds great with the bass guitar plugged directly into the input. Are the GEC power tubes the original tubes? They might well be, they look like 40 year old tubes. The ECC83 and ECC81 are EGROs, I don't know how old these are.

The interior:



Looks perfectly clean, considering this is a 40 year old amp! The solder points are covered with red lacquer. That means it was made in Harry Joyce's shop, right? If so, the amp must have been made in 1971 rather than 1970, since HJ took over chassis wiring in 1971 (according to the "HIWATT history" page on Mark Huss's site).

[OldSchoolDave]

Hi and welcome to the Vintage Hiwatt forum!

Interesting amp. I'm not as familiar with the earlier slave amps as some here, so take my comments with a grain of salt.

The back panel was painted that gold color (wonder why?). Perhaps it was done by the same person who replaced the Bulgin jack with the IEEE.

The GEC's do look very old. It's going to be difficult to clean the dust off without destroying the screening. Before you try, look for any date codes that might be stamped around the base. Regardless of whether or not they are original, if they are functioning well, they're worth a bundle.

I would expect to see mustard caps where yours has those pinkish-brown ones. Did the slave amps use different components?

Looking forward to reading some expert opinions which, I'm sure, will follow.

Dave

[riba2233]

Very nice! Also, if were you, i would replace electrolytics ASAP.

And how come IEC mains plug is female? It should be male for safety.

[Dr.HI-TONE]

Welcome!
Very Cool Amp. You are correct with the age/date and transformer dates.

[mhuss]

Nice piece. Congratulations.

I suspect the 'normally mustard caps' were replaced at some point, it looks like the paint is missing from those solder joints.

I second the motion on replacing the can caps, they must be ripe by now.

The GEC KT88s are of the same generation as the original factory tubes even if they are not the originals. Highly desirable as long as they are in good working condition.

--mark

[Dr.HI-TONE]

I believe the chicklet caps to be original.
I have seen lots of Hylights from the teens (12xx-19xx) with those caps.

[Energy]

The amp works fine and sounds good, as far as I can tell. So I presume the KT88s are OK, just a little dirty.
The amp was being used regularly by the previous owner in the past 35 years. But anyway you're probably right about the caps needing to be replaced. I'll bring the amp to a well renowned tech in my area (Tube Amp Doctor) for maintenance. Should I have the KT88s replaced, too? If they work properly, they might as well be used....

[Dr.HI-TONE]

I would pull the KT88s and save them for a rainy day. JJ makes a nice KT88 that is reasonably priced. When the JJ's wear out, they are easily replaced, you could spend a fortune to replace those GEC's.

[Hamtone]

How does a slave amp work when none of the ap amps have a slave out jack, at least not that early?


Cool amp brother

[Dad3353]

How does a slave amp work when none of the ap amps have a slave out jack, at least not that early?

Good evening, Hamtone...
At the time, slave amps were not intended for the guitar, or bass, but rather for the PA system. All the pre-amp/eq etc is supposed to be in the mixer desk (or PA head...), which could pass the resulting signal into one, two, or however many slave amps were 'daisy chained'. It's only later that guitar/bass rigs had outputs for this, as you rightly indicate...

[menace2u]

So how would you modify a VHR DR504 to drive a slave amp? Asking because making a modifying an original would be blasphemy!

[riba2233]

So how would you modify a VHR DR504 to drive a slave amp? Asking because making a modifying an original would be blasphemy!

Probably like this: (add a slave out with two resistors)

[Hamtone]

So how would you modify a VHR DR504 to drive a slave amp? Asking because making a modifying an original would be blasphemy!

Probably like this: (add a slave out with two resistors)

A master slave set up is about the best way to split your wet dry rig and sounds great.

[Energy]

Coming back with a question for the tech experts:

So I swapped in the JJ KT88s and measured the BIAS. I could not go lower than 48 mA, then I reached the lower limit of one of the onboard trim pots. So I adjusted the BIAS to 48 mA for both pairs of KT88s. Anyway, I'm wondering if the BIAS might be a little high? I noticed the amp is getting quite hot when running.
The plate voltage in a DR201 (same power section as my STA200) is supposed to be 650V, right? That would result in a plate dissipation of ~31W. Not too much, I presume - maximum for the JJs is 42W according to the data sheet.
Anyway I'm a little concerned about the amp getting so hot. Is that normal? How do you bias your DR201/STA200?

[mhuss]

Just the heaters of four KT88s dissipate 40 watts. Add 120 watts of idle tube dissipation, and you have something approaching a small space heater.

70% idle dissipation would be 29.4 watts, so 31 watts is not too extreme. You could also increase the series 22k bias resistor to 27k or 33k to increase your bias range.

--mark