BH5 Head and Combo

These are the Latest High Build Quality Valve Amps from China.

The Chassis is 1.5mm Thick Steel, Welded Box Construction. Correctly Rated Electronic Components, Very Good Transformers and a Through-Plated, Double Sided PCB. The Circuit Design is Text-Book, Cathode Bias, Single Ended, using a '12AX7' Preamp Valve and an 'EL84' Power Output Valve. Bias Settings are 'Middle-of-the-Road' and the HT Voltage is SPOT-ON. The Amps are Really Well Built, the Best I have ever seen out of China. Sadly, they are let down by a rather high level of BUZZ and HUM in the Circuit. Other than the 'Noise' Issues, this is a 1st Class, Top Quality Product.

The Amp's Output is a Healthy 5 Watts RMS and the PEAK Power Output is just over 10 Watts. 

So before I can start any Hot Rod work, I have to clean up the Buzz and Hum Issues. Once that is done, the Amp is Superb, and Wide Open to some Great Modifications. The Addition of ‘Power Scaling’ and ‘PS1+PS2’ to these Amps puts them in a 'Class of their Own' and allows the Amp to be used in any environment, From your Bedroom to the Stage.

The Combo Amp (BH5-112) is Fitted with an 'Eminence' Custom Blackheart Speaker. It's 12", Rated at 70 Watts, 16 Ohms and is Excellent Quality. It Works well in this Combo and Sounds Very Good.

Since their Introduction, I have Modified MANY of these little Amps and they have proved to be Solid and Reliable. Even at the 'Modified' Price of around £300, they represent Exceptional Value for Money.

Modifications

Some or All of these Mods may be fitted - Depending on The Final Price.

1. Power Scaling - This is the Business and essential for an Amplifier used in the Home. I Have tried ALL of the other systems that claim to Reduce the Volume without changing the Tone - This is the ONLY one that really works. 'RAT Electronics' is Licensed by ‘London Power’ to Install this Technology and Pays a License Fee for each Installation.

2. PS1+PS2 - - 'PS1'....This is the Standard Method of 'Power Scaling' in which only the Valve Output Circuits are Scaled. The Preamp Circuits are 'Held' at Normal Supply Voltage - - 'PS2'.... This Setting Totally Changes the Dynamics of the Amplifier as Both the Preamp and Power Amp Circuits are Scaled. The Resulting Effect is Known as 'Brown Out'. The most Well known user of 'Brown Out' was 'EVH'. He used a 'Variac' to Achieve the 'Brown Sound', but the End Result is the Same as 'PS2', without the Risk of any Damage to the Valves. Most 'RAT' Amps are Fitted with ‘PS1’ and ‘PS2’ as Standard.

3. Dual Output Valves - The Amplifier is Fitted with 2 x Different Output Valves, usually an ‘EL84’ and ‘6L6GC -or- ‘6V6GT’. You can Switch between the Valves for a Totally different Amp Sound.

3a. Dual Output Valve 'MIX' Function - This System is based around one Rotary Control. The Amplifier is Fitted with 2 x Different Output Valves. The Rotary Control Allows Selection of Just One Valve or the Other (EL84 -or- 6L6GC) -or- Any 'MIX' Between the Two Valves. Using the 'MIX' Control you can get a Great Bit of 'Brit Crunch' (From the EL84) Mixed in with the 'American Clean' (From the 6L6). This Modification Requires the Output Transformer to be upgraded to a Hammond 125DSE.

4. Twin Rectifiers - The Stock Mains Transformer already has the Required ‘Tap’ for a Valve Rectifier. Once the Valve Rectifier is Fitted - You can Switch Between the ‘Silicon Diodes’ -or- ‘Valve Rectifier’. The ‘SAG’ Produced by the Valve Rectifier Sounds Superb.

5. New Output Transformer (OPT) - The Stock OPT is Very Good but not as Good as a ‘Hammond 125DSE’. Changing the OPT will offer Better and Tighter ‘Bass’ Response along with Cleaner and Clearer ‘Mids’ and a Much better Defined ‘Top’ end. These Transformers are Expensive but well worth it.

5a. Dual Output Transformers - The Amplifier can be fitted with 2 x Different Output Transformers and a Switch to select the one you wish to use. This makes the Amp Loads More Versatile. 

6. Master Volume Control - If the Preamp Valve 'Bias' is set Correctly, a Master Volume Control will allow - Preamp Overdrive Only -or- Power Amp Overdrive Only -or- Both. Fitted to all ‘RAT’ Amps.

7. Variable Boost Foot-switch - This is a Foot-switch with Built-In Gain Control. You can set Just how much Gain you want with A Rotary Control located next to the Push-Button On/Off Switch. It Works Great and Gives you that extra 'Kick' when Needed. A Red LED Illuminates when 'Boost' is Selected. There is a Trade-off when using the Variable Boost. The Higher the Boost is set - the Less Effective the Tone Controls Are. In Practice this is not a Problem because at 'Full Boost' the Tone Network is 'Flat' and allows the Sound to Cut Through Nicely.

8. Because of the Hum and Buzz Problems, I have to Remove all of the Rotary Controls from the PCB. The Stock Controls (Pots) are OK Quality but just to be sure I replace them with Bigger '24mm Alpha Parts' and 'Hand Wire' them back into the Amp Chassis. I have Totally 'Re-Built' the Tone Stack - it can Completely Remove the 'Treble', 'Middle' or 'Bass' from the Signal (if required) - It Now Replicates a 'Fender Twin Reverb' in Operation.

9.  Preamp 'Bias' Switch - This Switch Changes the 'Bias' on the Preamp Valve to one of 3 Settings. Position 1 is 'Sharp and Bright', this setting makes use of 'Negative Feedback' (NFB). NFB keeps the Amp 'Clean' by feeding some of the Speaker Output Signal 'Back' to a Previous stage in the Amp circuitry. This creates a 'Cancelling' effect and reduces Distortion and Volume. - Position 2 is 'Clean and Mellow', The Preamp Valve is Biased for Medium Distortion with a Bit more Bass. - Position 3 is the 'Medium/High Gain' Sound, Early Distortion, Great 'Crunch'. The Harder you Drive it the Better it Gets.

10. Line Out Socket - The 'Line' Signal is taken from the Output Transformer.

11. Headphone Socket - The Speaker Outputs are Muted when standard Stereo Headphones are Connected.

12. 2 x Speaker Outputs and Impedance Select - The Output Transformer offers individual Speaker Outputs of 4, 8 and 16 Ohms and this Must be Correctly Matched to the Speaker/s in use. The Stock Speaker Outputs are Very Confusing and you can easily make a Mistake connecting your Speaker/s. The 'RAT' Setup is Simple and Straightforward to use - Connect a Speaker or Speakers and select the Correct Impedance - Done. Fitted to all ‘RAT’ Amps.

13. There are Several 'Other' Modifications that I do to All of my Amps that are Exclusive to me and both Enhance Performance and Help to Keep the Noise Levels Way Down.

The Background 'Noise' from the ‘BH5’ Amp is now so Low, you may not notice it is Switched on.

Short 'Power Scaling' Sound Clip