ivanrichards

Welcome back ! Hopefully we are now back into a routine of publishing a fresh blog every week. In this week’s blog, we discuss a major upgrade project recently completed for the (Fender) ’65 Deluxe Reverb Reissue, which we will refer to as the DRRI. The guitarist in one of Sydney’s best loved and longest surviving blues bands has been playing through a Twin Reverb for decades, but decided to downsize to a lighter amp for the smaller rooms, which makes complete sense, and invested in a new (2015) DRRI.

As you can see from the photos, this particular Limited Edition DRRI looks very smart indeed, with the early ’60s Brownface amps cosmetics. Also included in the Limited Edition package was a Jensen (new production) speaker. All other aspects of this amp were identical to the standard edition DRRI.

Unfortunately, the tonality presented by this amp was very thin and rather shrill. Overdrive characteristics when the amp was turned up (no pedals) were actually pretty awful. We attribute a lot of this to the choice of speaker. Just as critically for our customer, the lack of headroom with this amp and speaker combination defeated the whole purpose of investing in this particular amp, as it was virtually unuseable even for the smaller gigs.

The first step in this project was to upgrade the speaker, as is so often the case with combo amps. Choosing a speaker is not as easy as it sounds – there are a bewildering number of specialist guitar speaker options out there now. WGS offer some excellent choices at very reasonable prices, and we ended up choosing the G12C from their American Vintage range. We could just as easily have chosen the G12C/S for a smoother, softer top-end, but this model does seem to complement the DRRI voicing and adds a couple of dB in efficiency which will help with the headroom problem. Most importantly, the G12C fills out the missing lows and mids of the DRRI and behaves itself very well under overdrive conditions. The 75 watt rating of this speaker allows a healthy overload margin.

Having restored the basic tonality of the amp with our new speaker, in consultation with the customer we devised a major upgrade project to increase the headroom available by implementing a conversion from the existing 6V6GT output valves to the larger 6L6GC output valves. To take full advantage of the larger valves we also replaced the existing transformer set.

The available space and the need to allow clearance for the 12-inch speaker restricts our choices somewhat, but by re-orientating the output transformer and choke just slightly, we could install the power transformer, filter choke and output transformer set as per the 60’s Vibrolux/Tremolux series 6L6 amps. Such a reproduction transformer set was available at very reasonable pricing from Magnetic Components of Chicago, USA, although the cost of shipping adds quite a bit these days.

Such an upgrade will increase the power output of the amp to between 30 and 40 watts, as per the original amps of the abovementioned series, without a huge increase in the weight of the DRRI. It will be necessary to modify the bias circuitry slightly (one resistor) to increase the range of the bias adjustment to accomodate the 6L6 output valves. We also upgraded the main high-voltage filter capacitor to the good quality F&T brand.

This was not an inexpensive project by any stretch of the imagination, but much, much cheaper than selling the amp on and reinvesting in a more suitable amp. We have replaced the shrill and brittle tonality, as presented by this example, with a very warm, full sound, still characteristic of the best examples of the Fender Deluxe Reverb, and increased the headroom significantly. This is now a fine performance amplifier which will serve our customer well !

Hello again. In this week’s blog we look at correcting some electrical safety issues in a Classic Cat 1×12 combo from Bad Cat amplifers, of the USA. This particular Bad Cat would appear to be a limited edition, maybe even a one-off custom order, and we could find no reference to it at all on their website.

Most Bad Cat and Matchless amplifiers are derived in some way from (or inspired by) vintage 1960’s made-in-UK VOX amplifier circuits. This model is completely different, and is obviously derived from 1950’s Tweed/Fender and Valco/Supro amplifier designs. Classic Cat controls and functions are really sparse – just a pair of input jacks plus volume and tone controls. That’s it ! The design follows the classic Supro pattern of a pair of 5881 or 6L6 output valves, cathode-bias, for a nominal output of 24 watts rms at the onset of clipping.

There is a single 12AX7 gain stage followed by interactive volume control and single (“tweed”) tone control. The effectiveness of the tone control depends on the position of the volume control and also offers no control at all over bass or lower midrange frequencies. This stage is followed by a 12AX7 valve employed as a “paraphase” (self-balancing) phase-inverter, very similar to some mid-1950’s Fender (“tweed”) designs. However, this type of phase-inverter is not known for achieving perfect balance or low distortion, and so adds to the raw vintage character of the amp’s performance.

Our good customer Danny brought this amp into the workshop to resolve some electrical safety issues. The most obvious sign of trouble is the broken IEC 240V power inlet. Further investigation revealed a lost earth connection, plus a loose mains fuseholder which could not be tightened. This latter component was also not compliant for 240V in the first place. We replaced the IEC inlet and installed a dedicated chassis earth point. We replaced the dodgy fuseholder with a compliant component and installed a T1A fuse.

The amp now passed the Workcover NSW electrical safety test with flying colours, meaning that we achieve an earth test of less than 2 ohms from the earth pin of the 240V plug to any exposed metal part on the amp. You can see from the next photo the IEC inlet and fuseholder wired correctly, plus the dedicated earth connection to the chassis. The final photo shows the internal layout of the chassis, and hand-wiring Bad Cat/Matchless style.

We would like to thank Danny for his continued custom, and for supplying us with the subject matter for this blog. We offer world-class service, restoration, repairs and advice re most boutique level valve (tube) musical instrument amplification.  It HAS been a lifetime obsession.

Please check out our earlier blogs re amplifiers by Matchless, DR-Z, Landry, Jackson, Morgan, Matamp and others, plus our own Richards custom design amplifiers.

Welcome back to the blog, everyone. We have been servicing the Peavey Classic Series 30 watt and 50 watt combo’s since their introduction back in the 1990’s and we are in fact still the A.M.I. authorised Peavey warranty repairer (valve/tube amps only) for NSW. Since the 1990’s the 30 watt 1×12 combo has overtaken the 50 watt models in terms of popularity as they provide reasonable performance in a compact package. Reliability has been questionable at times – we have had to repair printed circuit boards (PCB’s), replace transformers, valves and 9-pin valve sockets, and so on. Bias for the EL84 output valves is non-adjustable, which means some amps run rather hot.

The subject of this blog is a more recent 2×12 model delivered to us by a local music shop, reported as losing output and nil reverb level. It may not be immediately obvious from the photo, but the speaker connection tagstrip, normally pop-riveted to the speaker basket, has come adrift, causing unreliable operation. This is a problem we have witnessed many times with the cheaper OEM speakers supplied by Eminence of the USA to various amp manufacturers. The only reliable solution is to carefully drill out the remaining body of the pop-rivet and refasten the tagstrip by other means.

In the meantime we isolated the ‘nil reverb’ problem to the reverb tank itself, which is mounted in a vinyl bag at the bottom of the cab. The only way to gain unrestricted access to both the problem speaker and the non-functional reverb tank is to remove the speaker baffle completely from the cab. This is what is known as a ‘floating baffle’, with mounting screws along the top and bottom front of the cab, which must be removed. The amp chassis has to be removed before this can happen, of course.

Once the baffle is removed and placed face down on the workbench, we can repair the speaker. We choose to refasten the tagstrip with nut/bolt/lockwasher rather than another pop-rivet. It takes longer but will survive the demands of rock’n’roll guitar. The other speaker on this 2×12 baffle is checked OK.

Before we re-install the baffle into the cab, we will repair the reverb tank. One of the transducers tests open-circuit (O/C) and is not repairable, so we will replace the unit altogether. This is not a bad thing as we will upgrade the reverb with one of the ‘MOD’ tanks, The reverb will sound much better than it did previously.

Reverb tanks are available in various combinations of impedances and delay times, so it is important to select the correct unit for the individual amp. In the Peavey Classic Series, the reverb tank is driven by an IC, requiring a different input impedance than for example a Fender ‘Deluxe Reverb’. The replacement tank is placed within the vinyl bag, which provides some degree of isolation from vibration, which in turn is screwed into the bottom of the cab. The baffle and amp chassis are each reinstalled into the cab, and the reverb cable reconnected within the amp.

We had previously tested all the valves (tubes), external to the amp, and also carried out a power output test and electrical safety test. The final play test revealed a huge improvement, and the amp was returned to the music shop. Thanks for checking out the blog and we are located here in Gosford (Wyoming) NSW for all your valve (tube) amp service needs, including custom design. IR.