ShortScale.org

The TSL 100 has (a) no reverb to speak of, though turning up the reverb does introduce some hum, and (b) a noise-introducing circuit known as the Virtual Power Reduction circuit. The eBay seller has offered a reduction of £75. Seems like a reasonable deal at both ends - he doesn't pay the full price of a workshop repair and I have a budget that should more than cover the costs.

The reverb crcuit appears to use a quad op-amp driving the tank through a phono-connected cable and the return (again through an RCA-phono-connected cable) goes to a 4558 op-amp. So that all looks cheap enough apart from the tank. Will check out the tank tonight, I hope.

The Noise Introduction Circuit is another matter. Trying to identify which part of the circuit it is is fun....

I wouldn't even attempt fixing the VPR. That's a job for Marshall.

The reverb isn't tube driven? It's most likely the tank itself or the leads.

Oops, it's not a 4558 like elsewhere in the crcuit, it's:

Mitsubishi M5201. This is like a dual op amp with a switch, a DC control voltage on one of the pins (DIP pin 1) selects the output from one of the inputs, and passes it to the output stage.

NJR makes two compatible parts, the NJM2120 and the NJM2121. Search mouser.com for NJM212* to get price and data sheets.

Hoping it's the leads...

Reverb tank prices (assuming it's Accutronics 9AB2C1B 6-spring <aka 3-spring> medium delay)

Allparts - £20.82
ampcomponents.co.uk - £36.
Torres Amps - £42.50

The stock tank in my DSL50 sounded like ASS, I put a smaller, fatter, 2 spring (or 4, looking at your description of that other one) jobber from an old Laney head into it, sounds a load better.

SO BEAR THAT IN MIND.

Hmm, well... crappy contacts on the tank phono sockets, cleaned them up a bit and it all measures good but no improvement. Reverb starts to hum after several minutes on and no response to a wet finger on the cable. Testing was a bit interrupted by decorating but tonight I guess we'll try replacing the cable first and then measure some voltages/scope some waveforms. The tank is a twin line (quad spring) model.

VPR looks like it open-circuits a bypass to some 680K resistors on the outputs of the phase inverters, resulting in a reduction in final drive level. Sort of two-position post-PI master volume.

Overall, amp is noisy for the first few minutes on. Need to open her up and see what gives, I think. JJ EL34s and EH 12AX7s fitted.

Nothing wrong with JJs.

Mike wrote:Nothing wrong with JJs.

Glad to hear it. Can't find the site I was on where someone was ranting that they don't make tubes like they used to in the good ol' USofA and he'd had to replace the tube bases on some JJs (not EL34) with some GEC bases because the bases weren't built to the correct tolerance.

I think my eyes just exploded. What rot.

I'm impressed you're soldering on with this alone, I wouldn't go dicking about with a TSL personally, too much complicated shit I could break/kill myself on.

Mike wrote:Nothing wrong with JJs.

Indeed, I've been running a pair of JJ E34L's for a few years with zero problems, and have used their ECC83s since day one.

Here we go:
http://www.timeelect.com/400-faq.htm
Questions 3 & 4 in the FAQ are about using GEC 6550s vs. other makes.

Excerpt:

Are all 6550's the same?

No, for the following reasons.
With the way tubes are being made in other countries today, there is little chance of any of the same type of tubes ever being the same.

There are no unifying standards behind what they produce. There simply are no unifying standards to cover their manufacturing methods, material standards, or electrical performance characteristics.

In the USA we had government specifications, with industry's material standards and testing practice for the vacuum tube and electronics industry to follow. Not all tube companies were qualified to supply specific vacuum tube products to the government of the USA.

OK, I took the chassis out of the case, reseated all connections to the reverb board and reverb now works fine.

We're left with noise which starts bad, may get worse and then reduces in bandwidth (like turning the treble down) after 10 minutes or so, leaving an occasional pop and introducing a slight hum. Sounds like a bad cap to me. I've confirmed that it's in the output stage by removing the phase inverter - this doesn't affect the noise. I've also removed output valves to eliminate individual valves and associated individual resistors. So it's in the HT smoothing or in the bias smoothing. Muist get the scope to the amp to check.

Crap, trying to find suitable replacement caps isn't fun. Mouser looks like the best bet so far, and I'd hoped to upgrade to high-temperature (105C) ones too.

Existing caps are 330uF 315V Samwha HC and 100uF 350V Samwha SD, both HC and SD ranges being 85C types.

Need to check OD/lead pitch as Samwha offered a range of form factors for the same capacity and volts.

Also considering replacing the 220K bleed resistors that (a) ensure the HT is balanced across the series caps and (b) make sure the HT is non-lethal within a minute of switch-off - of course, local Maplins only have 2 of the 4 that I need.

NickS wrote:Here we go:
http://www.timeelect.com/400-faq.htm
Questions 3 & 4 in the FAQ are about using GEC 6550s vs. other makes.

Excerpt:

Are all 6550's the same?

No, for the following reasons.
With the way tubes are being made in other countries today, there is little chance of any of the same type of tubes ever being the same.

There are no unifying standards behind what they produce. There simply are no unifying standards to cover their manufacturing methods, material standards, or electrical performance characteristics.

In the USA we had government specifications, with industry's material standards and testing practice for the vacuum tube and electronics industry to follow. Not all tube companies were qualified to supply specific vacuum tube products to the government of the USA.

There's a world of difference between being proud of your country exporting good quality products and 'USA > Everybody else'. The latter seems incredibly common for a lot of guitar gear (guitars, tubes, pedals etc.) I've seen some boutique pedal companies justify prices by saying they're hand-made in the USA with 'quality components'. The neglect to mention the components are probably chinese. I don't think the point really needs to be made on here, but snobbery based on country of origin is rarely justified with guitar gear.

I would say that the JJ EL34s in this TSL 100:

(a) have (solder?) lumps on the side of some of the pins
(b) have pretty flat ends to the pins.

Neither of those should affect the sonic quality, but they do make those valves look rough and unfinished compared to the GEC KT66s sitting in my drawer, and the sharper edges on the ends of the pins probably result in a bit of a scrape as the valves push into the sockets. That may improve contact but reduce socket life.

Component size is critical as the electrolytics on these PCBs are packed together like those on a computer motherboard. After much searching I found suitable caps at both Mouser and Digikey, both US-based. I decided to take the plunge and order from Digikey. That's about £13 of parts and £12 of carriage, VAT "payable on delivery". I'm taking the opportunity to upgrade to 105C Nichicon and Panasonic, and use longer-life-specced parts where possible. Whether I get hit for VAT depends on whether HMCR decide to include carriage as part of the value, as they're entitled to but don't always do.

I doubt a TSL100 has ever been this pampered.

NickS wrote:That's about £13 of parts and £12 of carriage, VAT "payable on delivery".

Watch these feckers, if it's FedEx, they'll try and sting you for a £6.80 admin fee too, for doing pretty much fuck all. I argued them out of it, but they were bastards.

benecol wrote:

NickS wrote:That's about £13 of parts and £12 of carriage, VAT "payable on delivery".

Watch these feckers, if it's FedEx, they'll try and sting you for a £6.80 admin fee too, for doing pretty much fuck all. I argued them out of it, but they were bastards.

Tell me more, tell me more. Did they put up a fight?
Ah-hah, ah-hah, ah-ha, ah-hah..

Who did you have to argue with? I heard of someone who got charged, took it up with Digikey and got a refund.

£6.80 is relatively cheap for an admin fee. Parcelfarce and Post Office are like £8